I've no idea how effective this would be, but unless your mage is a fresh 70 and is pretty poorly geared, I don't see how it could work.

Since existing gems are destroyed when you re-socket an item (i.e. you don't get back the ones your replacing), you're faced with either maintaining two sets of equipment or coughing up for new gems specific to your mission each time you go out.

In fact, now I think about it, I don't see either option as cost-effective, even for a fresh 70, let alone a reasonably well equipped mage.

I reckon your best strategy is to just not get hit

Since I started making more intelligent use of my mage's pet for boosting my lowbies, I've cut my repair bills by 75%.

edit: clarity