what kind of containers are they in? besides "stickyness" being a problem, suction may also be a culprit. if the containers are flexible, you may be able to get a little air to the bottom by warping them.
other than that, try going for the heat diferential thing, as snoop pus mentioned. the greater the diference, the better the chance of success. since you mentioned that it can be frozen, i'd go ahead and do that, then place it in boiling or close to boiling water for a bit. if the container isn't glass or ceramic, some serious rapping may do it.
if all fails, perhaps sacrifice 1/2 inch or so of one end, by slicing it and using a spatula.