I tried a batch awhile back. The only thing I missed was the little red straw from an aerosol can. I put in a squirt oil can, it works really well. You can get acetone from a paint and body supply to mix with your ATF. Although a sureshot spray can might be overkill, you could get a smaller air powered sprayer.
However, there was an article comparing various penetrates in the April 2007 issue of Machinist Morkshop Magazine. They arranged a subjective test of all of the popular penetrants with the control being the torque required to remove the nut from a scientifically rusted environment.
Penetrant: Average Load:
none 516 ft lbs
WD40 238
PB Blaster 214
Liquid Wrench 127
Kano Kroil 106
ATF-Acetone mix 53
It's interesting to note for those of us that are too lazy to do the atf/acetone mix that Liquid Wrench results were close to Kroil at like 1/4 the price.

My batch has been sitting in its can for over a year with no loss of performance. I just shake it up before each use.