I've had this problem a couple of times and did the usual google search to find out what my options were,no doubt many have had this problem and judging from the google results just about everyone that has ever ran disc brakes
There is a lot of advice recommending that you chuck the contaminated pads and buy new ones,which can cost anything up to £20 per brake[if you buy recommended types]
Some recommend putting them in the oven for an hour or so till the solvent burns off,but for the most part that idea gets poo poo'd off as a bad idea which will cause more problems or even cause the abrasive part of the pads coming away from its backing.
Seems the majority of the bike shops will insist you buy new pads,although i have found 2 local that just use the oldest method and use a blowtorch to burn it off.and ive also asked a professional mechanic[m/bike] who also recommended burning the solvent off.I've also found in backshop chat over coffee that burning the contamination off is something that is known about but not to tell the customers .
Since ive been running discs on the 2 latest builds ive managed to get hydraulic fluid over every pad ive used
but just rely on my trusted blowtorch to sort the pads out and ive never had a problem or been forced to shell out for fresh pads
I put them on top of my bench vice and heat them till they catch fire,the flames are the solvent deep in the pad burning off.
Then its a gentle rub with 1000 grit W&D laying the paper on a piece of glass[mirror,picture etc] till the whole surface has been sanded.
I've now used this method enough times to be assured it works and works well.
I can't really comment on putting them in the oven as i cant see it being hot enough to cause the solvent to ignite
,i think it would just smoke[and stink out the house]
If you dont have a blowtorch then i think holding the pad by its backing plate and holding that in turn over the gas ring on a cooker should burn it off ok.
ALLOW TO COOL SLOWLY,DO NOT PUT THEM UNDER THE COLD TAP TO COOL.
so if your LBS insists on buying new pads.Find another bike shop
1976 Raleigh Chipper,1991 Muddy Fox Adventurer, 1992 Raleigh Diablo ,1992 Rudy Project, 1995 Cannondale M200 ,1997 Santa Cruz Tazmon ,1997 Specialized Stumpjumper ,1997 Specialized Rockhopper ,1997 Marin Quake 9.0,1998 Marin Pallisade trail ,1998 Raleigh Torus,1999 Orange Clockwork , 2005 Kona Hahanna , 2010 Orange Pure7
The Marvellous Mechanical Hope Collection