dabac

I say you can.

One of "my" webshops lists two different spacers for use together with Shimano 7-speed cassettes on 8/9/10-speed bodies, one is listed as 3 mm and one as 1 mm.
According to them, sometimes you get away with only the 3 mm (I did), sometimes you need both. From that source 4.5 mm isn't even mentioned.
I've once improvised a spacer by making a thin coil of steel wire and placing it over the body before putting the cassette back on. It worked just as well as the real thing, so I left it there. Took a few tries to get the diameter right though.

But if you're set on shooting for 4.5mm, then your current 2 mm spacer + a spacer scrounged from a disassembled Shimano 9/10-speed should get you really darn close.