There is a small App called "Hide IP", you do however have to remember to run the app before logging onto the poker site.
I"m not sure if this would work, but if your together, then missus could try running it.
It"s not ilegal, and it gives a false ip(as opposed to your own).
Again i don"t know how this would work after a router or hub? Perhaps one of the mods may have more idea?
Hope this helps.
BTW, wouldn"t it flag, if your both registered at Betfair on the same address anyway?