a lot of chemical companies have a foaming
soap for the entrance of tunnels, i would think you could probably use that product, it shouldn't cost to much
I have a wiota tri foam in the bays at one of my washes, and the weep system is built in (we don't use it- its too mild over here) but i wouldn't think it would be too hard to pull off. Many of my tri foam customers put it on before the foam brush use anyway, so adding a snow foam/presoak would be a good idea by my estimation.