Can a Boc protecting group be removed with trifluoroacetic acid?
If you do a literature search (SciFinder/Reaxys), it seems that HCl in polar aprotic solvents (dioxane, THF, ether) are the 'standard' conditions for this cleavage. 

You mention that you require the TFA salt, not the HCl salt, but even if you use HCl to carry out the reaction, its fairly trivial to get rid of the HCl and then convert the free amine into whatever salt you desire. 

(Though as vapid said, your reaction conditions are probably quite important, and you might find if you just push the TFA reaction a little harder you can force the Boc off).