The thinness of the growler would be my concern too, there are ways around the potential cap leaking.
I don't advise doing this, BUT - I'd be tempted to add 2 TBS of sugar to a growler full of water, then add some baking yeast. That should get you up around 4 volumes of CO2, more than you'll need unless you are bottling something like a hefeweizen which I would definitely not do in a growler. Put it in a bucket with a lid and wait a couple of weeks. See if it explodes.
Even though that is more pressure than you are likely to need, you want some margin of safety in case one growler is weaker than another, or in case you bang them together.
Again, I don't think this is a good idea. For one, they're not made to be used that way. For another, 64 oz is a pretty big commitment! You're better off with 22 oz bottles or even champagne type bottles.
If you try it, let us know what happens.