Arctic Silver thermal paste should be stored in the fridge, too; that also helps thicken it up for application, so it's easier to get the desired amount on the CPU. If you're worried about not that letting it flow into the groves properly when you seat the heatsink, drape a piece of paper over it (to help keep dust from settling on it) and let it warm to room temperature first.
I don't have time right now to look them up, but am I right in remembering that "Ceramique" is their thermal epoxy? That stuff seems like it would be just as likely to spill as the thermal paste, but the end result is the CPU and heatsink becoming one...forever.