In a word, no.
To the best of my understanding, the Minitor 2 must have the same "a" for both sets of tones it is listening for. (This is the only way I have seen them set up, when looking for two sets of tones, I could be wrong.)
If you want to have more flexibility in your tone detection, you need to go for a newer Minitor, or a non-Motorola solution. Newer voice pagers allow multiple frequencies, and multiple tone sets.
Keep in mind that only the Minitor 5 is the only Motorola pager that is narrowband capable, out of the box. (Swissphone and Apollo both offer narrowband capable units.) United Communications Corp. is doing after-market modifications to Minitors, to allow them to function with narrowband transmissions.