That depends on how small. If it's a monthly payment (like a credit card minimum) there's no reasonable way that constitutes value for money. (As it was, my credit union wouldn't even accept payment from Western Union -- whether you can use WU is up to the individual bank -- and a credit card company suggested a Western Union option which I'm not sure is available here and was about 13 usd anyway, which was a bit steep to send just a minimum payment.)
For a larger payment -- say several hundred dollars -- I would try Interbank, which charged me 19 usd to send money. Also, though they would have liked a DNI, they didn't insist upon one. And the money arrived in a day. (BCP wouldn't do a transfer without my opening an account there, and the costs at Scotiabank were roughly double as Interbank.)
If anyone knows of an easier way to transfer funds directly into a bank account, I'd be interested in knowing it.