Essence conversion

I feel like maybe there should be a way to convert your dust into the other variant.

For instance I find myself sitting from time to time with some champion essence that I'll likely never use and I just need those 50-100 cosmetic essence to craft the skin that I've stored in my hextech crafting inventory.

It wouldn't hurt the balance and would just serve as a neat little thing that makes life easier. Same of course the other way if you have a lot of cosmetic essence and really just want to convert some of it over to champion essence, so you can unlock your mastery badge 6 or 7.

I think a fair rate would be 2:1 or perhaps 3:2 if Riot feels generous. What do you guys think?