There is a another thread about Ace where I ramble on about the same.
Currently I do not think what you (and me) want is possible. Not a limitation with Ace, but how templates are handled in Hugo.
The brilliant @tatsushid added the Ace support, and I would be a happy puppet if we could find a way to make the base- and inner thing work.
I haven’t spent too much time thinking about it, it should be possible – just have to find the simplest path.