Thanks for the tips. It worked--I bought that multi leg itinerary and inputted my Advantage number and was able to choose all my BA metal seats. Oddly the bulk heads (the only seat to have in BA C) were all X'd out. I skipped the seat selection, bought the ticket and a few hours later I went into manage my booking, plopped in my PNR and viola all bulk heads seats were open and available for me to choose.