I mean, if you're sure of the eligibility, and that the inventory is available on an OD basis, then you could just book with your discount code on the AC website you normal itinerary without the stopover, then ask to change just that segment by calling in (change fee waived due to 24h rule).

But if anything breaks, you will be SOL and down a discount code.

But generally speaking, if the connection/flights work with the discount code, and the fare allows a stopover, and the inventory is available on an OD basis, then there's no reason for it not to work.