E1 9.1 Mexico VAT/Income Withholding - how do you drive it to more than 2 accounts?

HI --

In Mexico, we need to split the VAT Withholding between 5 different accounts (VAT - Leases; VAT - Services; VAT - Freight; Income - Leases; Income - Services).  From what I can tell, you can only set up the Constants (P76M005) for I and V once each to point to an AAI or you get a duplicate key error.  How do I drive the other three types of withholding to different accounts?  Is it possible to add new values to the 76M/WT UDC?  I noticed that the I and V are hard coded values... would adding new values even work?