I am looking to go to Costa Rica later this year. I'd like to go via the US, upgrading from WT+ to CW on the flights between the UK and the US, and flying in Business class on AA between New York and San Jose.

I can do this on the matrix ita system by simply inputting LHR-San Jose for WT+. This books into WT+ for the transatlantic legs and business for the legs between New York and San Jose. So theoretically if I could book this fare I could then upgrade the transatlantic sections (there is availability on the routes it books into).

However trying to do this on ba.com raises all sorts of problems. Selecting WT+ books into economy class for the American Airlines legs. It also gives me an exotic routing from JFK to San Jose via Madrid......

Obviously i want to MFU from WT+ to business at the time of booking. So my question is: is this intinerary bookable if i call the BA call centre, or is it a forlorn hope as it won't work online?