I'm no expert here and maybe this is a stupid recommendation but try multiple coats of polyurethane, the kind they use at the bars. Ever see a wood bar that's really shiny and gloosy? Look at it closely and there is about 1/8-1/4" of polyurethane sealer ontop.
I'm willing to bet (I' dont know for sure) if you spray a few coats of this on, sand it smooth and spray a light finish coat; the slide will be slippery as you want it to be.
Then for kicks and giggles apply floor wax to the shiny polyurethane and people will slide like the wind.
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