I just got in from a brief range session and cleaned my r9. I have been using a modified syringe technique that works well for me.
Placing the slide facing away I use both index fingers and both thumbs to squeeze the assembly and pop it right in.
I was getting pinched pretty good using one hand. It really does get easier once you become familiar, whatever technique you use.
Also, the frog lube ran great, cleaned up easily, and my fingers weren't all oily trying to grip the assembly.
I really love this gun.