Is it $400x3 tickets or $1200x3 tickets? if it's $400 per ticket, I'd just do a split order of tickets, putting 1 ticket on the first card, and the other two tickets on a different card and then call in to have the PNRs from each ticket batch linked later.

You might be able to split payment by calling into customer service, but I suspect there would be roughly a 0.5% chance of the credit card offer you're seeing now on the web to map over to a phone purchase like that.