Relax, have a homebrew...don't stress...you're making a non-monster beer, right? Just dump the yeast from the bottom of your carboy into the brand new zip lock (sanitize your carboy mouth if you used a stopper; if you used a bucket or a carboy cap, you probably don't have to sanitize the opening then). I double bag my yeast and I don't use the baggies with the zip tab plastic thingy. I use regular new zip lock freezer bags. When you get ready to pitch it, just dump it into your wort, aerate and watch it go. I've never had a problem underpitching or overpitching when using this method into a beer that's under 1.080. I don't separate the trub. I DO, however, make sure that the original beer I made using the yeast is clean and has no off flavors. I would be more cautious about trub if I was making a very delicate light lager and would worry more about the yeast counts if I was making a monster beer.
However, using your findings from Mr Malty, I'd say that a third to a half-full baggie would be right on the money.
I know great brewers who use this same technique with excellent results.
Try it and let everyone here know how the brew turns out.