Worty,
I realize the goal here, besides stopping wet sumping, is to save money. I also realize that what I say here is not going to change your mind about using a valve, but I still think it is worth saying. Assuming you are having this serious wet-sumping issue due to a well-worn pump, this pump, while serving for now, would be delivering a worse-than-original oil supply. It would continue to wear and, at some point, cross the threshold between adequate and inadequte supply. The reason for an SRM pump should not just be to stop the wet sumping. While nice (my bike sat all winter without a noticeable drop in level), I think the more important feature is better oil delivery at higher pressure. If your pump (for oil on the bike, that is) is in it’s golden years, the cost for a new pump will seem trivial if the old one gives up the ghost.