Component Pay-Benefits based on different rate then paid.

Has anyone worked with unions where the benefit is based on the standard base rate from the union rate master table but the contract calls for pay to generated at 90% of the base rate.  There are numerous contracts that reduce the negotiated base rate for certain jobs.   I was thinking of using component pay where a pay type could be generated which would represent the 100% rate and the benefits would be pointed to that component pay code.   Is there anyone who has dealt with union situations where the benefit is actually based on a grossed up rate?