Partial routing to a group

We have many groups (weddings mostly) who would like to route a portion of a guest's reservation to their group account.  We see there is an option to set a credit limit when routing to another individual, could this feature please be added to allow routing to the group.  

i.e. The couple wants to pay for $100 of the room charge for one night of a guest's stay.  Even though the room rate is $325, we want to route only that $100.