My best guess would be trying to use a windshield washer unit.
Do they run a third pump off the reservoir for them or do they come on in parallel with the front windshield washers? If so, then it would be a simple matter of splicing in a tee an adding the spray nozzles. IIRC, the washer reservoir for US has two pumps clipped into the bottom. Though you could probably cut in an tertiary outlet and remote a pump somewhere else if sufficiently motivated.