Hi xrok1 - one way you can do this now is to drag out a construction line along that direction, then click and hold on the little arrow that pops up, and choose "Project next point" on that menu. That will lock down the next point to be projected on to that direction.

Check out the construction line section in the docs here: http://moi3d.com/beta/moi_command_reference2.zip for more information.

I might be able to add a keyboard method for that in the future, but that one will have to wait for a bit.

- Michael