Until I bought my turkey fryer I had been using a ~7 gallon electric boiler which had been repurposed from its original job as a canning aid. Here’s the link: http://www.brouwland.com/shop/product.asp?cfid=28&id=2398&dt=24&l=2
I wasn’t able to find anything similar on Amazon, but maybe your LHBSS will have something?
Immersion heaters are plentiful but aren’t a good idea because the wort would contact the element directly and cause caramelization, off flavors, etc.
You could also (maybe) do an electric coffee urn, as long as it’s made of stainless steel.
FWIW, I lived in apartments for several years and always ignored the rules about BBQs and open flame. Put my Big Green Egg up there, which is a pretty obvious indication of fire, but nobody ever said anything (other than “when are the ribs done?” of course 
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