“I can imagine it working. Has DIY been tried before?”
It should be comparatively easy to build a system. IIRC the first evaluation units at RAE Bedford were hand-built from 3in plastic gas pipe, a good lens, and a red/white filter like a large 35mm slide. And of course a lamp, but not too powerful as it might melt the plastic pipe!
Most of the early PAPIs were portable; - a friendly manufacture might lend you a set – you found one.
Also, I recall some PAPIs were air droppable – self levelling systems for more obscure operations.
A note on the Research Engineers website who credit RAE with ‘devising’ PAPI. Whilst the BLEU/Flight System division at Bedford developed and proved many PAPI applications, the original idea came from a French test centre; a British ‘boffin’ had seen the units and commissioned some more for steep and two segment approach work. The subsequent development improved the all weather operations capability.