Just to close out this thread, it turns out that TunerCat 2.26 or 2.27 had the transient fuel flag mapped as one of the PASS-KEY flags (I forget exactly which one). I found it by accident when using TunerPro to do a diff against a stock GM file, and in TunerPro, the bit location (12028) was mapped to two functions. Looks like it's resolved in TunerPro $EEX v. 3.6 as of late 2015, but just for posterity's sake I'm posting on this thread.

It makes me wonder how many highly modified LT1 cars ended up with aftermarket engine management over the years because they turned off something labeled as VATS but was actually transient fuel and caused nasty tip-in leans...