This silicon putty:
withstands soldering temperatures, and can be used to hold components in place when you're doing evil things like expecting the solder to provide mechanical integrity (say, soldering header pins flat agains a board.)
(It's a pretty substantial-size package, especially since it's mostly re-usable. Unfortunately, smaller batches of silicone putties that I tried (ie "Silly Putty" are NOT capable of sustaining the same heat.)