Webby, unless you're determined to weld your fingers together 
Buy this...
http://www.ebay.co.uk/itm/BRAKE-CALIPER-PISTON-REWIND-WIND-BACK-TOOL-KIT-22-PIECES-car-service-tool-/181439011424?pt=UK_Hand_Tools_Equipment&hash=item2a3e9b9a60 
LMAO I should have mentioned I already purchased the tool as per the link's above 
I just like making home-made tools 
After I mentioned these tools on Thursday, I ordered one. At that price, it's worth having just in case.
As for making home-made tools, I have a lathe, mill and welders, so happily make tools when there is no alternative, or the cost/time don't add up. I made a tool for adjusting the V6 cambelt eccentrics as my 2nd-hand timing set didn't come with one. I bored the worn 1/2" drive hole of a 30mm socket big enough to take the torx socket and welded a slightly bent piece of strap to it to make a custom spanner, which cost nothing and took about 20minutes. Hell, I've a mate who says the repair he did on his dad's Lamborghini calipers paid for the milling machine he'd just bought. But that's hardly the case here, I couldn't make the bits for that sort of money, let alone the time that would be required.