You can buy Evo-Adaptors from Supercycles and use them, but a LOT of 4-bolt mount frames seem to not really allow you to run a 2-bolt magura on an evo, and actually get it so that something doesn't hit the tyre...
Anyway, take off the QR lever from the 2-bolt mount, and those plastic elbowy things that go on at the top of the clamp bit. Buy some longer bolts (usually about M5x60, but you might need to hack off the last 5mm or so of the bolts), and some washers.
Line up the top hole of the clamp with the top-hole of the 4-bolt mount. Whack the brake into the clamp, put the top bit of the clamp on, then stick one of the bolts down into the hole. Tighten it up as much as you can really, although not too much or too little 'cos you'll strip the threads on your frame. Which isn't fun...
Anyway, do the bottom ones up as you did the tops, really. Same as a standard Magura, and ta-da, you have a 4-bolt Magura.
Unfortunately, without bodging it's a F**ker to get the 2-bolt Magura boosters to go on the 4-bolts (although you can hack the bottom bits - where the booster is usually clamped - off the CNC'd Magura booster and use two of the triangly bits, but tyre clearance can sometimes be an issue there, especially with mods).
Also, you could just buy 4-bolt Magura clamps for £15 incl. p&p from CleanBikes. This would probably be more preferable, because not only do they look nicer, but also you can adjust the brake far, far more easily. This is because they have two slot-holes on the clamps - top and bottom - so you can adjust them in that way, whereas with the two-bolt clamps they only have a circular hole at the top, so you can't really move them at all.
If you want more info on what the F**k I just said here, PM me or summat!
Mark.