Sure. Open the Terminal Emulator. (if you don't have one, download from the Market -- Android Terminal Emulator, I think it's called. But I'm pretty sure I put it in the latest all-in-one package.)
Make a directory for APKs in your sdcard:
Switch to the root account:
Switch to the ash shell (to enable tab-completion):
Change to your /data/app directory:
Find the names of the packages you want to backup:
This will give you a list of all the packages you have installed. The ones you've downloaded from the market will (generally) be of the form com.author.appname.apk. The apps from the AndroidApps directory will also show up here. Disregard them.
For each app you want to backup, copy it to the directory in the sdcard:
Code:
cp com.author.appname.apk /sdcard/APKs/
You should be able to just type the beginning of the file name and hit tab to finish it. (i.e. com.auth<tab>)
You can also do this via ADB if you have it installed and working (and that way you don't have to type on the phone keyboard at all).
You can also do it by mounting data.img on any system that can read an ext2 image.