However, this wont work. If there's an ad for Coca Cola, the whole reason why Coca Cola is paying the podcast host is so that the message would get to the listener. If anything, the money should be shared with Coca Cola, and not the podcast host - who has been paid already (for sponsored spots).
And at that point, it just becomes user paying Coca Cola directly, with you in the middle.
It is an inefficient system.