My first thought, that Anneintherain already articulated, was that it sounds like the ideal situation would be for him to find a gf/FWB/playmate to swing with him. My understanding (I have no experience) is that swinging is, in general, fairly M/F couple focused, so guys operating solo are pretty much out - BUT, in a poly-type dynamic, I don't see why the female of the couple would have to be the wife.
A common mistake (that I have made myself a number of times) is to equate "fair=equal" - i.e. that both sides have to look the "same" in order to achieve "balance". I think the goal is for everyone involved to have the freedom/opportunity to have their needs met and live their lives in a way that they personally find fulfilling and satisfying. This does NOT mean doing things that you don't want to with in order to "make" your partner happy.
I'd make the analogy with some of the BDSM threads I've read here - say wife wants to explore BDSM but husband doesn't. In a monogamous situation this would mean that one or the other doesn't get what they want or they have to compromise. In a non-monogamous situation? Fine. She explores BDSM with someone else. In my mind, a good example of the "one person can't be everything to another person" idea.
Me: poly bi female, in an "open-but-not-looking" Vee-plus with -
MrS: hetero polyflexible male, live-in husband (together 21+ yrs)
Dude: hetero poly male, live-in boyfriend (together 3 yrs) and MrS's best friend
Lotus: poly bi female, "it's complicated" relationships with Dude/JaneQ/MrS; married to TT, poly male
VV and MsJ: bi-women with male primaries, LTR LDR FWBs to JaneQ
My poly blogs on this site:
The Journey of JaneQSmythe
The Notebook of JaneQSmythe