Hollow skirting boards?

There's a big assumption in many of the replies so far that you're asking about mains cabling - and if this is the case then I think you'll have realised by now that this is not permitted without adequate protection.

IF, however, you're talking about e.g. low power data / CAT-5 cabling, a seemingly more and more common issue as time goes by... then why not manufacture your own?, buy the skirting board that you want, turn it over and run a router, set to cut a sensible depth, down the rear face to machine out the cable-way that you desire.

p.s. You'll still accidentally drive a nail through the cable, eventually.

Regards

Mike