thanks for the tips all. I ended up arranging a SWIFT transfer via my Postfinance account to my US account, then having my US bank cut the check direct to IRS for me. A bit of a hassle, but at least I know the steps for next time. I also enrolled with EFTPS (didn't initiate in time for this payment) so that for future payments I can forgo the check and have the transfer direct from bank to IRS.