Sure... you could do it a couple of ways. It will probably require some hand coding, though.
One way would be that when a specific purchase is made you could set a session variable and set it equal to say, 1 if the right kind of purchase is made or 0 for everything else. Then in the attachment line for the universal email, create an "if" statement where if the aforementioned variable is equal to 1, then the attachment is the result... if the variable equals zero, that means they didn't make the purchase to get the specific attachment so you could either have a different attachment or no attachment at all.
Cheers,
Brian