Is this at all possible for the 1992-1996 Camry to convert to the ES300? The body shape is kinda similar, and mechanically it's the same. Has it ever been attempted/done?

I've never heard of this conversion being done, although plently of people had asked for it. I'm pretty sure if you searched long enough online, you'd probably find something about it.

Its been done.
http://img54.exs.cx/img54/1690/kuria6.jpg
http://img54.exs.cx/img54/3194/kuria1.jpg
Thats a Scepter (Camry) wagon from China. Im sure someone on www.toyotanation.com knows how to do it. Thats where I got the pics from...but make sure you do a search on the topic before posting the question. Youd surprize yourself.