Paying for flights (or other things) in dollars with Paypal

I am in the UK but have a US dollar balance on my Paypal account.  Given the exhange rate, the more I can buy in dollars the better.

I am wodnering, could I book a flights on a US website, and pay with Paypal? Would this be enough of a bargain anyway?

I have a Paypal debit card that's set up with my parents' US address as a billing address, which I use to purchase things that require a US billing address, including flights from US carriers that don't accept non-US cards, like AirTran.  However, I've never carried a £ balance on my account - I've always converted to $ - so I don't know if my situation is in any way similar to what you're proposing.