All agreed. Provided he would be happy to work with 'components' (the diodes), rather than off-the shelf 'electrical accessories' (DP switch modules), the approach you suggested is the simplest, and certainly the cheapest of of an of those which have been proposed to the OP.I fully concur with your comment but the purpose was to satisfy the writer's requirement in a simple and (not particularly unusual) cost-effective manner
My only regret is that I didn't think of it, particularly given that I got 'almost there' with my comment about diodes and AC (my only excuse being that I wrote it 'in the middle of the night' ) !
Kind Regards, John