Participant in tax treaty countries

A participant who is transferred to a country with which the US has a tax treaty (the Netherlands in this case) wants to continue to participate in the 401(k) plan.  He would remain employed by the US employer but would pay taxes in the Netherlands under the US/Dutch tax treaty.  I am struggling with 415.  If the wages have to be includible in gross income for purposes of 415, does the fact that the tax treaty treats the wages as Dutch taxable mean there are no wages for purposes of 415?  I know that the wages excluded under 911 are added back in for 415, but that's not my concern. These wages would be excluded under the treaty not 911.  There is a savings clause in the treaty providing that the US can double tax, does that  make the wages includible for purposes of 415?  I know this is done all the time and that I must be missing something obvious, but I don't know what it is.

I think it's good income for 415. See Treas. reg. sec. 1.415(c)-2(g)(5).