It may be prudent to prepare the blade by sawing in a candle before sawing into the aluminum. The stearine or candlewax will significantly reduce the sticking or "build-up"of aluminum on the sawteeth. Repeat as neccessary.
Spraying with WD40 works, but is less effective. Dipping in kerosene works OK, but poses a substantially bigger fire-hazard.
Waxine lights work very good, as the waxine has slightly better anti-build-up properties then does stearine ( normal candlewax ) but although they're abundant over here, I don't know if theyre readily available where you live.
1/8" should be readily sawable without support, but when sawing thinner, like say 1/16" I would recommend you follow Forrest's advise and use some light plywood to support the material - between the sole/base of the saw and the aluminum. So when sawing from underneath ( a common way to use a barrel-grip jigsaw ), the metal would be on top. When using a sacrifical board, the waxine/stearine will be soaked up in an alarming rate, so keep some handy during the cut. Sawing from underneath, it's easy to apply some - just lightly touch the blade while it works. But mind your digits please...
Regards,
Job