You should be able to bend the sensor so that it will fit into the 
sparkplug's recessed hole. Use 2 pairs of pliers for this.

Put the compression ring back on after you have slid the sensor on the
sparkplug. The sensor is made from soft metal and will tear easily when
you try to torque down the sparkplug. Moreover, without the real
compression ring, you will get blow-by. Tighten the plug carefully! In 
fact, tighten it only slightly, then take it back out and look how much 
damage you've done to the sensor. Repeat over and over with increasing 
torque until you think damage is bad enough. :)

--
Sami ('75 Westf.)
dakhlia@wuecona.wustl.edu
http://wuecon.wustl.edu/~samid/