If you have a piece of tubing, you could very easily make a blowoff tube. Or if you don't have any tubing, if you are using a bucket, you could also un-snap the lid and loosely place it on top of the bucket, then place the bucket into a bigger tub to collect any overflow. If it's in a carboy, remove the airlock and loosely place some tinfoil over the opening, and place the carboy into a tub to collect overflow.
"Stop giving me credit for those stupid quotes! For that last time it wasn't me! STFU NOOB!" <-- Benjamin Franklin