Proper tool for less than £10 I inc. shipping on Ebay
G clamp is another good alternative which I've done dozens of times without issue
http://www.ebay.co.uk/itm/SYKES-PICKAVANT-66065000-HYDRAULIC-HOSE-CLAMP-TOOL-FOR-BRAKE-FUEL-LINES-HOSES-/201065559081?pt=LH_DefaultDomain_3&hash=item2ed070f429
By the time you take the caliper off, then mess around finding and fitting a nut, you'll have lost so much fluid on the floor and allowed air bubbles to leak in.
Not a good idea.