Interesting - I suppose that will do it, although the sidecut will kind of make it hard to keep even. It's worth a try I guess.
I'd almost rather leave the factory grind than use a file though - I learned a lot about ski edge tuning from my friends who have kids in race programs. Anyway, he told me the key to a good edge is a good surface finish, and that means hitting the edges with many different "grit" levels. The ones I just did I sharpened the base edge and re-cut the side edge.
The cutting I did with a panzer file, then I went to a bastard file. The shapening/tuning is done with two different grit diamond stones and finally a really fine ceramic. The panzer and bastard leave a very rough finish which tends to dull quickly - the mechanics of this as far as I can understand is just the physical breaking of chips on the surface that are left from the rough cut.
Apparently if you get a very nice surface finish with no burrs, you actually have a sharp, and strong surface which will not dull easily. Then you just need to go back and touch it up with the diamond stones and ceramic to get it sharp again, unless you whack a rock and take a chunk out, in which case you are supposed to clean with a ceramic to remove the work-hardened material, and then perhaps remove some significant material i.e. re-cut the edges to get it out. You could just say hell with it and leave it, but that's apparently the proper way. It's important to clean those strikes before you file though because the file will have a hard time cutting the hard spots.
Anyway, based on that, you could just sharpen in the way you explain with just running a diamond file along the edges. It's pretty easy to hold them straight without a guide and they don't remove much material at all. Also you don't need to worry about hard spots - diamond is the hardest material known to man.
I was going to do a little write-up based on what I've learned about edges but there is no shortage of it on the net, and it all says basically the same stuff I would say with some small differences.
I'm not sure I'm going to invest in all that stuff as I don't see the point for my metal-edged XCD skis. Perhaps just a diamond file to touch them up.