Hi,
I just remembered that in newer version of Netweaver (I think it's since 7.31) there is a new BADI that allows you to populate user values in SU01. So if your CUA has it then you could try to replicate your spread sheet logic in this user exit. Depending on spread sheet complexity it should not take more than 1 day to implement.
Also in CUA you can use BAPI_USER_CHANGE to change user's attributes in central system. If you set it up in a way that attributes will get replicated to child systems then it should work. Again, writing a simple program that does this should not take too much time.
Cheers