If you can find a second (which should be easy, the wikidot has a list of where they are) then you can just do the following.
Go to the items menu and select leave. Leave 1. If you have infinite items on then you should still have two, but one will be on the ground now. Pick it up, you have 3. Repeat, but always leave 1 less than you have. If you attempt to use or leave all of a stack then the infinite items doesn't work.
The same can be said of upgrading. If it costs 5 to upgrade, and you only have five, it will consume the 5. If it costs 4 and you have 5, the number you have won't change with the trainer.
It wont let me leave the item. is their another way? :/
Edit: I moved them to the box and it duped them with the trainer activated, thank you.
[Edited by imsolegit, 10/11/2014 12:02:21 AM]