I'm in a similar situation actually.

I'm currently waitlisted for BA98 on SEP13 and confirmed on BA92 on SEP14, both WT+. Apparently WT+ is booked out on BA98.

I phoned up BAEC to ask if it was possible to upgrade the BA98 flight with miles to J so I could relax in CW (flat bed yay!). They said there was no upgrade availability. When I asked about cash they told me to phone again and try another option. I have no idea what this would cost.. is this along the lines of £70~100 like CE-upgrades or in the hundreds of pounds?

BTW these bookings are also TA bookings, and the TA says they don't do upgrades.