Thanks for the answers. But I think I wasn't clear. I want to use the \subref command not the \ref one (supported by default on LyX). The difference between them is that \ref produces "1a" while \subref produces only "a".
I need to cite subfigures in the caption of the main float. Example.: Fig(a) --- Fig(b) Figure 1: Here you see some figure (a) and another figure (b). Got it? But now I'm almost sure LyX really doesn't really support it. If so, this is another good (and simple) improvement for LyX 2.1. :-) Cheers, --- Diego Queiroz