A self-employed person can deduct health expenses against gross income. You are correct in that COBRA cannot be deducted in this way. But it can still be taken as an itemized deduction. I'm not a tax accountant, but my tax accountant is. Another gotcha: if you're taking the 60% markdown on COBRA from Obama, then no, you're not allowed to write it off at all, but I wouldn't be complaining about that.
Only the portion which is greater than 7.5% of your gross income can be deducted on Schedule A.
If you have a HDHP with an HSA you can pay COBRA from the HSA tax free.