When you reach the PSI level required to unlock a new ability, you can use the bacon to pause whatever you're doing and train it immediately.
How do you get back there, however? I was in the middle of Lungfishopolis and the entry point to that is well within the depths of the semi-dry lake floor. I can't just walk back there.
Best Answer
Turns out that to get his attention I need to simply walk to him and press F to use it on him. You then get the option "I'm ready to go back into the field."
The problem is that if you have an item equipped and press F, what will happen is you will use that item on Agent Cruller. You can unwield your item by pressing X.