That completely depends on what you mean by "not too much modification"...
the mirrors don't bolt to the skin of the door, there is a piece of metal inside the door that they bolt to. Now it would be completely possible to make a bracket that uses your existing bolt holes, but has more bolt holes to mount the new mirror to, that would be the easiest way in my opinion, and would not take drilling extra holes in your door.
You'll need to have both mirrors available, so you can figure out the shape and dimensions of the bracket, then if you have no way to do this (i'm guessing you don't since you're asking about this) get the shape drawn up and measurements on it, then take it to the local metal shop and have them make it for you out of 1/8 inch metal.
Or you could just drill holes in your door and put some metal on the inside for it to mount to. I'd personally make the bracket though, that way you're not damaging anything on the truck permanently.
anything can be made to fit anywhere (within reason). If you find a cheap source for these mirrors, please remember me... I broke the mirror on my 2000 powerstroke and they were really expensive the last time I checked (Like $300 bucks each).
Reason I ask is because I found some guy selling a set of the 99-00 Super Duty mirrors for $10 for the set. I don't really care for them, if you want them you're more than welcome to 'em. I haven't bought them yet, but if you wanna set something up we could figure something out. He lives about 60 miles from me.
Here's the pic he has listed on the ad: