2002 Grand Cherokee WJ Laredo 4.0L

I've done a ton of research on changing out my heater core. I know there is a great 3 part video on removing the dash along with a step by step tutorial in wwjeeps.com.
There is some info out there that suggests you can replace the heater core without discharging the a/c system. Basically some say you can take apart the air box while on the truck to access the heater core. Of course it's a bit more difficult to get the old core out and new one in but I really won't want to monkey around with the ac.

Has anyone out there replaced the core without evacuating and recharging the ac system? any tips, tricks or pics would be greatly appreciated.
Thanks!
Mark