Here my proposal, use Z for parallel constraint given the visual similarity (the parallel lines in the letter) and switch to G+P to call polyline and P to change modes.
Another option could be to use S+M (switch mode) key combination and add some code to ignore the M in the task dialog when this shortcut is used.
Also another option now that I think about it is to change parallel constraint to K+P or symmetry to K+S
Thinking about shortcuts a doubt came to my mind, what happens with the rest of the shortcuts when we have a tool active? currently we change from rectangle to circle easily with the shortcuts, will this be lost with this feature, making an intermediate esc mandatory?
Inviting abdullah to this