eschew ->eschewwing!??!?!? oh hell no
'eschewing' is correct I think. From the question you asked it was the only answer that I could come up with off the top of my head: and it doesn't fit your rule!!!!
Sorry Joseph, there is no real rule on spelling conjugations. Any rule you make will break down. You are better to just remember the words that you use often, and buy the biggest dictionary you can find for the rest.