no, you can't do it directly.
The best you could do is put the guy you would want as the back half of the Tandem as your Long A (and don't set anyone else to Long A). Then start your Starter 2B to a low pitch count (perhaps a max of 60 pitches?) Assuming the Long A is rested, he should always be the first reliever to come into the game, unless it's a blowout, in which case your mop up may come in instead.