Unfortunately there is no way to label the touch strip buttons.

However an undocumented 'feature' that makes the built-in labels slightly more useful is as follows:

Press and hold any of the touch strip buttons and the popup label will appear, however instead of releasing your touch, slide your finger up or down the touchstrip. As you move over the other buttons each popup label will appear in turn so it is an easy matter to review which of the buttons you wish to activate when releasing your touch.