So, you want to open a screen session in an ssh login session from within a local screen session, eh?

That's right ... this is my fu, so the situation gets to be as convoluted as I want. Here's how I do it:

~/.screenrc
-----------
escape ^@^@
bind ^@ other
bind ' ' other
hardstatus off
hardstatus string (%n.%t)
hardstatus string '%{= kG}[ %{G}%H %{g}][%= %{= kw}%?%-Lw%?%{r}(%{W}%n*%f%t%?(%u)%?%{r})%{w}%?%+Lw%?%?%= %{g}][%{B} %d/%m %{W}%c %{g}]'
termcapinfo xterm*|rxvt*|kterm*|Eterm* 'hs:ts=\E]0;:fs=\007:ds=\E]0;\007'

Now, that changes the status bar to a suggestion gleaned from the Gentoo wiki (and displays it in xterm/gterm/whateverterm's title bar).

The most important part in the context of this topic, though, is the "escape ^@^@" bit. That changes the screen control character from [aA] to space.

The two bind lines remap CTRL-A-A and CTRL-A A to CTRL-SPACE-SPACE and CTRL-SPACE SPACE ... to toggle between two screen windows in your local session.

There you go ... space on local, regular on remote.