I don't see why not....instead of starting with the dremel for the initial cut you can use the drill, just make sure your bit makes a large enough hole for the jigsaw blade to reach through.
Also, a problem is going to be that your holes will be so small in comparison to the large window done in that above "how to" you probably won't be able to cut the entire hole in one shot, the corners will be too tight. You might have to pre-drill the corners and then use the jig saw to cut corner to corner in a straight line. I don't know if that makes sense when I put it into words. I would do that frequently with small cuts in wood work before I got my dremel.
Dremel would definitely be easier...no one you can borrow one off of eh?
Here are the cuts I made on my 900, note the cut in the top right drive bay so that the case wiring can be tucked behind the drive when it's inserted....the top fan power supply wire can also be tucked through there. Cuts like that may be tricky without the dremel...but the straight forward ones in the case should work..i'd think.
here is after the sanding, priming and painting. I wanted to cover the bare metal that was exposed from the sanding to remove burs.