Has it ever been done? Is it even possible? Trans-mounted FWD has been the Honda standard forever. So wouldn't converting the CL to AWD be a little more complicated than bolting on a transfer case and drive shaft for the rear wheels? It would be a whole new platform, right?

 

Transverse-engine AWD cars:

Acura (MDX)
Audi (TT, A4 1.8t)
Mitsubishis (Lancer, Eclipse, 3000GT)
Lexus (RX300)
Honda (CR-V)
Mazda (Tribute)
Ford (Escape)
Volvo (V70 Cross Country)
Jaguar (X Type)
Toyota (RAV4, Highlander)
Kia (Sportage)
Pontiac (Montana, probably)

There's more, but can't remember off the top of my head.

To send any power to the opposite (read: rear) end of the car you need a subframe of some sort to support the differential and hang the suspension bits off of. The burlier the subframe, the more power can be put through it (RWD cars have very burly subframes, as all power is sent through the rear, which is what accounts for most of their extra weight). Rarely are FWD-intentioned cars converted to AWD; the majority of the time the cars were designed from the outset to later accommidate the subframe, the only exception that I can remember is the Mondeo platform being converted for X Type duty. But look how well that turned out.