I just had a nice conversation over the phone with Daniel Lafontaine who is a luthier and also an electronics nut head. He has designed a pickup that you jam between the bridge and the table, like on the drawing on his site: http://perso.wanadoo.fr/lutherie/capt.htm.
Interesting, no ? Mr Lafontaine says that it gives good results pizz and arco, nice acoustic double bass sound. I'll organize a demo at my luthier shop (F. Bonnier) to check it against Schertler, Underwood, FWF, and my Bass Max (all hail BG). More later.