Probably not very much help, but supply does sometimes change.

I was looking for two award seats seats in F (alternatively J) to Cape Town for Jan-March 2006. A month or so ago, there were no J seats at all for that quarter and only the occasional F. (There was availability via JNB using Comair internally, but they are not available for AmEx vouchers, and cost more in so-called taxes and charges anyway.)

I ended up booking two award seats in VS Upper Class instead, using 198,000 VS miles instead of 150,000 BA miles plus £30 offline fee.

Yesterday, I did a 'what if' for a colleague, and found availability in F or J on nonstops to CPT for perhaps 20% of dates in the first quarter. Too late for me, and I don't know why there is availability now. It may suggest availability may improve for you.

By the way, a similar situation applied last year when I was trying for CPT for this April. Nothing in F or J with BA for our dates. Actually, they did us a favour, as we used DL miles (only 160,000 for the pair and far lower 'taxes and charges') for 2 biz seats with SAA, a far superior service to NCW with better beds and on-demand video.

Nevertheless, I too would like to be able to use AmEx vouchers on routes that I want and I find the inability to do so one more frustration with EC.