IMDB says that, in Episode 7, they were originally going to use just Anthony Daniels' voice for C3PO but he insisted on actually getting into the costume for real. I thought he always HATED wearing the costume? 
I mean, that one time he met Alan Tudyk, Daniels was so jealous of Tudyk being able to wear a simple motion-capture suit - vs. the uncomfortable C3PO suit - that Daniels cussed him out for it (Tudyk even said that getting a "Fuck you!" from Daniels was a high point of his career
).
So what's up? If Daniels hated wearing the costume so much because of how uncomfortable it is, you'd think he'd jump at the chance not to have to wear it...

I mean, that one time he met Alan Tudyk, Daniels was so jealous of Tudyk being able to wear a simple motion-capture suit - vs. the uncomfortable C3PO suit - that Daniels cussed him out for it (Tudyk even said that getting a "Fuck you!" from Daniels was a high point of his career

So what's up? If Daniels hated wearing the costume so much because of how uncomfortable it is, you'd think he'd jump at the chance not to have to wear it...