Sub-accounts at OpenSRS are not the right way to transfer ownership.
You can move the domain into a new ownership profile for no charge (perhaps this is really what you are saying), but if you use a sub-account, you either:
1) Don't give them access to all features in the domain manager
or
2) Give them access to all the other domains in your ownership profile.
Neither is the right thing to do to the domain owner.
-t