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I think the border between legally recognized and religiously recognized marriage is confused too often. In the church sense, gays in the US can get married depending on the church. If the state doesn't recognize the marriage with legal rights, that is no reason their friends, family, and even moderately associated acquaintances cannot recognize them as a married couple.
The solution then, is to allow the man (or woman) to marry their first spouse, and list the other spouses as dependents on tax-returns. However, the spousal tax advantages should not apply, simply because this could be abused easily, and work-provided health insurance should only apply to the first wife (changeable in the event of death or divorce) because it would be too expensive for a company that provides spousal health insurance to provide 1000 policies to a man with 1000 wives.
However, other important rights, such as hospital visitation rights, should be provided. Medical decisions should be made via voting between the wives. Also, asset distribution after death would be an issue. Writing both a living will and a last will would largely take care of these things. The only hard part would be getting the hospital to recognized the extra spouses as "family".
But should the government recognize additional spouses? No.