I echo what @Mark Wiley says - I believe there is a flag you need to pass to include distributions or not, but it is an all or nothing transaction.
When dealing with custom distributions, I find it easier to let GP do it's own calculations, then use an eConnect post procedure to handle manually updating the special cases. This sounds like it may be much easier for you to do than to replicate the entire distribution from it's source.if you're new to eConnect - it allows you to update existing stored procedures that fire either before your transaction (pre), or after your transaction (post). you can find them in the GP company database, and are named ta<transaction name>POST i.e. taPOPRcptHdrInsertPost. The OOB versions are just stubs, but you can add on whatever business logic you need to, and can pass a few variables from your transaction XML to the stored procedure. They fire synchronously with each of your XML transactions. The trick when using these is to remember to re-create them after you run any upgrades on GP as the upgrade process overwrites any customized eConnect stored procedures.
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