If someone is willing to pay a large amount of money to influence a programmer, they'll be willing to manually negotiate / transfer it (rather than doing it through gittip).
I think all that is needed is a link that says... want to tip more? then donate directly to programmer by mailing him. This will remind the donor that he probably could give more... see how many people opt for this and figure out the nature of the donations.
That way, the service remains simple and manageable and won't end up being a money laundering operation for some terrorist.
