My initial thought is to just have Spacebar be the toggle for locking a newly aligned, constrained element within the Family Editor. It could be any shortcut, if there was an option within the keyboard shortcuts for it.
For example:
I align a line to a reference plane, the lock shows up, I hit spacebar. Done.
When you have a lot of constraints to add, it's a pain to lock everything with the mouse. If there was a keyboard shortcut option, that would be great!