Modify T3 Bulb for a T4 Socket
It is not safe to operate the bulbs in the wrong sized socket. The loose connection can produce arcing which will cause heating of the connection and could very well lead to fire. 

There really is not a practical way to safely replace the pins either. Even though some LED models may appear that it would be possible to solder on different pins I would advise against it. And it is likely that you would either damage the pin attachment points or that obtaining the correct materials ends up costing nearly as much as just getting the proper bulbs.

Safety should not be supplanted by frugality. Get the proper product for the application. Return the product if possible as suggested by Tester101 in the comments. If not returnable then eat up your mistake as a bad investment and learn from it to look more closely at what you select for purchase.