One thing you can do is insert a Timecert -
http://www.timesert.com/ .
These are pretty easily installed and are approved and used by Porsche.
They are plenty strong as this is Porsche's approved method of repairing stripped cylinder head stud taps on the block - if they can hold the cylinder head torques, they'll definitely work in this case.
Depending upon what you pay your mechanic, it may well pay you to buy a repair kit and do it yourself. Afterward, you can either add the tool to your toolbox - there are several other areas on the Boxster which benefit from timecert repair, or do what I did - get the kit, make the repair (in my case a stripped swaybar mount tap) and then resell the kit on eBay (I sold mine for the same price I paid, so essentially a free repair).
Cheers!