Does the PT185 have any downslope, or is the arc always suddenly off when you let off the torch switch?

If it has some downslope, it could be set up to weld aluminum with the torch switch OK, although a foot pedal is always nice when welding on a table or bench, etc.

You might recall this aluminum flooring in a boat project I posted up a while back. Check out the last two pics of the first post, for example. Welded with a torch switch and manually varying the duty cycle with the torch switch, and with some downslope dialed in:
http://www.everlastgenerators.com/fo...-(jakeru-s-10)

I don't think it would work nearly as we'll on a machine that doesn't support any upslope or downslope, though.

But yeah without a means to taper off the current, you'll need to go really fast near the end. Probably best to stop, let cool, then finish in a subsequent arc lighting (and repeat as needed) in such a scenario.