I if you take great care when you cut the channels in the foam, save the pieces that you removed. Stuff the wires into the channels, and if you carefully trim the foam strips that were removed, you can use some CA to tack those back in covering the wires. But just tack them in with a dot of CA spaced every inch or so. That way, if you ever need to remove the wiring, it will be easier than if you glue it back in solid. If you take care doing this, after you paint, you can't tell were the wire tracks are.
Another method is to fill the tracks over the wires with DAP lightweight spackle. I use this all the time on my foamies if I get a dent or hole in the plane. It is so light, it will not add enough weight to the plane to be noticeable. I buy this at Lowes or Home Depot.
Bud