Beedub, why? The reason for losing the electric setup is to lose the weight, doesn't mean it can't be done. It won't be out of the box, but a lot of these things require some innovation.
peddy, as above, I doubt you would be lucky enough that they would directly mount onto the BMW electric rails. You may be able to get an engineering company to fabricate a plate to sit between the two - yet more weight through - I know some guys who've been prepping track cars and have had to get creative - although this is usually mounting the Recaro (or similar) rails to their cars where things don't always line up. Personally, while I don't think it's impossible, like Beedub, I wouldn't bother, you'd only really have the back and forth adjustment anyway which is painfully slow!
I think this is a good mod - I like my M Sport seats, but think they have been oversold somewhat. You can buy Poles already trimmed in leather although alcantara is more popular as it's less slippy.
If you look under the Motorsport section on PH there are quite a few race seats available for sale. Think there may also be a seats section under parts. Could be a good option if you're going for a re-trim anyway.
ADD: Personally I like the idea of getting them in alcantara and just having the seams stitched in a different colour, maybe a diamond pattern on the back like the BMW Performance ones, which are awesome! I'd be tempted to get the door cards done similarly.