This works for me:
Assign _Enter to a mouse button. I’ll call it mouse button 5.
Start new model.
Start Polyline command.
Left click four times to create a polyline with three segments.
Click mouse button 5.
The command completes and a polyline with three segments is created.
The following is in the command history window:
Next point of polyline. Press Enter when done ( PersistentClose=No Close Mode=Line Helpers=No Length Undo )_Enter
Can you provide a detailed description of something that does not work when using the extra mouse buttons?
If you put _Polyline as the mouse button command, does pressing that button start the Polyline command?