Don't know the answer to your question but from the t&c linked to the voucher in the BAEC account it says:
"Redemption Vouchers must be booked via BA channels only, these being the BA Call Centres and online at ba.com."
nsr, wow, that would make a big difference to me, as I do primarily open jaw trips. Is this T&C clause stated just when you actually get a voucher credited to your account or did you find it somewhere on the BAEC website? I just wish Dilly would step in and answer the question one way or another, as I'm not the only one who has asked it.
Thank you for indicating there is some hope here.