Can you offer suggestions for a thesis statement for a critical essay on "Archaic Torso of Apollo" by Rainier Maria Rilke? My thesis statement (and supporting evidence) must be shaped from information "within the poem" and cannot include any outside information about Rilke (such as inspiration he may have had from working with the sculptor Rodin). I've read this poem a dozen or more times and what I get from it is Rilke's appreciation of the beauty of the human form and how his use of imagery and simile makes the statue seem alive, but I'm having severe "writer's block" when it comes to developing and properly wording a thesis statement that makes "sense." I'm not even sure if I'm on the right track.

You are off to a great start with your thesis idea. A formal thesis statement encompassing this idea could be worded as follows:

Through his unambiguous interpretation of the subject matter at hand, Rilke both expresses appreciation for the beauty of the human form and acknowledges the idea that art comes to life through observation.

A thesis on this subject might be organized according to the four stanzas of the poem, each of which expounds on the central idea in the thesis statement. For example, the first stanza suggests that although only the god's torso is presented in the sculpture, it holds a life of its own. This life is described by Rilke as "a lamp, in which his gaze, now turned to low, gleams in all its power." This clever use of simile illustrates the personification of the torso that characterizes this poem. By isolating his subject matter, Rilke proves that facial expressions and literal eyes are not required to experience the "gaze" of the sculpture.
In the second stanza, Rilke notes how the "curved breast" of the sculpture "could not dazzle you so" if the work was not "suffused with brilliance." He also describes a "smile" that runs through the sculpture's hips and thighs, hinting at the theme of virility that is both implied in the work and a part of Apollo's nature. This simile is particularly important as supporting evidence for the thesis statement because it demonstrates Rilke's ability to understand the true nature of the subject matter with the limited visual information presented by the sculpture. 
After gazing at the sculpture for so long, it has taken on a life of its own in the poet's eyes. With none of the typical human indicators of emotion and expression to draw upon, such as the eyes and mouth, the poem implies that the observer is able to see the true spirit of the work. Without facial features, the sculpture smiles and dazzles. Despite being made of stone, it exudes warmth. These lifelike qualities characterize Rilke's perception of the torso and allow the reader to see the subject through an entirely different perspective.
In the third stanza, Rilke notes that "Otherwise this stone would seem defaced" without a head. This line implies that the sculpture itself is imbued with life that gives it more personality and expressiveness than mere stone can produce. In his eyes, the stone glistens "like a wild beast's fur," further solidifying the poet's rugged, almost animalistic interpretation of the piece.
In the final stanza, Rilke comments that the sculpture has "burst like a star" with light "from all the borders of itself." This line draws the conclusion the entire poem has been building towards: the torso has exceeded the bounds of its limited form and taken on a life and nature of its own. Without examining or referencing any outside sources, it is reasonable to speculate that Rilke views the torso as a case study on the nature of form in art. Rilke describes his experience viewing the sculpture as interactive, one in which he begins by assessing the work only to find the assessment turned on him. This is exemplified in the lines, "for here there is no place that does not see you. You must change your life."
By discussing these themes, which present themselves naturally throughout the structure of the poem, you can craft a strong essay without relying on any outside analyses of the work.