Yes it can be done, and I have it!!! Unfortunetely you can't just add the wiper stalk with the variable controls and have it work. It's been tried and it was a waste of that person's money (though a boon for us in the info. dept.

) I had a member of another forum make a controller for me so I could have variable intermittant wipers. It taps three of the wires in the wiper stalk's wiring harness (in the plug, no cutting wires) and has a timer controlled by a potentiometer (read: knob) that's mounted on the side of the steering column. It works anytime the wiper stalk is in the "off" position and is negated as soon as the stalk goes to one of the working positions. It did require drilling a small ~1/4" hole in the column cover however everything can be easily removed and the hole filled with a plug and no one's the wiser. It only took a few minutes to install.... really the longest part was deciding where I was going to ount the knob.
I use it all the time when it rains and it works great. Sure it would be nice to have the control on the wiper stalk, but this is a good alternative. If you're proficient with elecronics then you can probably make one of these yourself with parts from Radio Shack. I'm not, so I relied on Bill and he took great care of me.
Here's a pic of the controller he built
And here's a pic of it installed