Sotto, by default ViEmu uses its own marker, not VS's selection, to highlight the visual area.
There is a command to turn the current visual range into VS's selection: gS.
Thus, if you select an expression and type gS<F9> you should get the quick watch (as long as F9 is the hotkey).
You can also set up a ViEmu mapping to do the whole thing, using :vscmd to call the VS command directly:
:vnoremap \\ gS:vscmd Debug.QuickWatch<return>
Will assing the reverse backslash key to converting the current range into a VS selection and calling VS's command to pop up the QuickWatch window. You can use any free key combination (not taken by VS), such as <C-S-F2> for Ctrl-Shift-F2, etc...
You can insert this command inyour _viemurc for it to be applied on every session (the file should be a plain text file in your home directory, check %HOMEDRIVE% and %HOMEPATH% to see where that is in your case).
Regards,
-- Jon