I can't find any hard facts on the actual pressure rating for a 1/2 gallon growler. Northern Brewer says specifically not for use with carbonated beverages.
http://www.northernbrewer.com/shop/1-2- ... -of-6.html
But this is the standard container for take home sales from a microbrewery, off the tap. With the understanding to keep it cold I suppose so little danger for yeast reactivation.
The PolySeal caps will hold some pressure. I've trouble with the metal ones leaking.
Those flip tops Jimmy uses seem to be thicker glass to me and probably have a pressure rating.
I say go for it with some precautions. Put a bag around them just in case.
PS. Lots of guys also use 2L plastic bottles. They hold LOTS of pressure.