Using 'dynamic' to save lines
The prevalent answer is: No. (Funny enough, working with Office files seems to be a valid exception to the rule).

The problem is that you don't have type validation anymore, and any issues will reveal themselves at run time.

I'd say, if it's a small thing and it won't be touched or changed by people who might not know how it works, go for it (Even then, make sure you document this).

Otherwise, an Interface approach sounds like a better idea, like ChrisWue's comment said.