Some hotel frequent guest programs will allow you to "launder" miles. I know Hilton Honors is one of them. The problem is the exchange rate isn't very favorable. I believe Hilton will double your UA miles when you turn them into points, but it's converting those points into AA miles that gets you--something like 5 points=1 mile, although I'm not 100% sure. I think Starwood may also allow some form of mile laundering, but I don't know the details. If I were you I'd probably just convert the miles to points and use them for HHonors rewards.