I don't think it's possible to set one up until you live here and can prove residence. It's a bit difficult for some when they even live here. Most of us start out with basic accounts to begin with that sometimes don't have checking or debit cards and have to show our reliability for a number of months since we have no credit history at all in the UK before the accounts are broadened. I think the UK is fairly strict though about not allowing it so people aren't just setting up off-shore type accounts.
You may want to look into other ways of doing the transfer. There are lots of threads on here about the best way to transfer bank account funds, some have used things like XE Trade, others setting up Paypal US and UK accounts and transferring through there--although there are some risks with Paypal sometimes freezing suspect transfers for some time while they investigate them. I can't remember other options off-hand, but if your bank won't work with you, your best option may just be to set up a new US bank account that is more friendly to overseas transactions.
Cross posted with Ksand24: I hadn't thought of the passport accounts as most I know opened them after coming here as well--just because they struggled to open accounts with no credit. If that works, it may be an option, but they don't give you a lot for the money they take, which is annoying.