My employer W2 doesn't have any social security assuming I'm clergy. How do I pay my social security? I have a W2 so a 1099 might double count the income.

My employer says I should just claim clergy and not pay social security.  But I want to pay into social security.  I'm trying to find a way to pay it when my W2 has none withheld.  No, they won't reissue a W2 with social security withholding.  If I claim self employment, it will show the income twice.  Is there a form for just paying social security?  Thanks