Yes, I did this recently. Phoned up to get a quote (which they had to request from the fares team) so had to call back the following day to find out how much the FTV would be.

Then simply applied for the FTV via the online form as normal.

Frustratingly the voucher - when it comes through - doesn't actually make any reference on how much it's worth - so worth keeping a note of what they say on the phone.

Really impressed really, as I've effectively got a transatlantic one way flight for the price of half a return, rather than the normal extortionate price you'd get for one ways.