It's rather hard to do it. wmctrl needs to know the window title in order to operate on it, but it is damn hard to know the title of any terminal emulator, be it gnome-terminal, rxvt, xterm...
- Often .bashrc specify PS1 to change window's title to current path.
- editor like VIM changes window's title to the current file.
- command line tools like mosh love to change window title.
- ssh into another machine, usually the shell (bash) on the remote host changes the title. So if you remove title-changing part of PS1 you need to do it to every computer you may connect to -- a long list of which for any seasoned sysop.
- Even if you run GNU Screen in a terminal, the session inside screen can still change the title of the outter terminal emulator.
fluxbox exceptionally allows referring to a window by other properties of the X-window (xwininfo) than title. but switching to fluxbox is too big a change for this small need.
In short, there seems to be no way to know the title of the terminal emulator window ... or, is there one?