Sharpening big slicks

Has anyone come up with a good (ie easy) way to sharpen the big, old-fashioned slicks? I've got two, 3 1/2" and 4", and since the biggest stone I have measures only 2 1/2" across I have a hell of a time getting a true, straight and sharp edge. So I always end up sending them out to a machine shop, which removes a lot of the steel every time they sharpen them. None of the jigs that came with my Tormek grinder are big enough to handle them either. Any ideas?

Thanks in advance...

Dave

I use the "scary sharp" method: http://www.shavings.net/SCARY.HTM
I made my own jig out of some aluminum parts I had laying around. In this photo, I'm doing a chisel, but it works for the slick, too. http://home.mn.rr.com/bremer/Sauna/sharpen.jpg

Good Luck. CB.