Sorry that I misunderstood your original post.
I can't find anything specific on this, but I'll give you my opinion and how I reached it.
It's clear in Publication 535 that a self-employed individual can deduct insurance premiums for themselves and their spouse. The unclear part comes when your spouse, as you've said, enrolls in Medicare. But the publication is again quite clear that Medicare premiums can be deducted, as well.
Now...your wife's Medicare premiums (deductible) are not in your name. That said, I'd think that any supplement plans that you've purchased for her (in her name) would also be deductible.
If it were me, I'd go ahead and use those Medicare and Medicare supplement premiums as deductions. As long as the primary criteria for using the SE Health Insurance Deduction are met for your business, I believe you'd be safe doing so.
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