Actually the KLM Intercontinental Crown Lounge has showers, but the lounge is only available for KLM and NW Platinum Elites.

But you could always post your travel dates in the KLM forum and ask if somebody might be there on your travel dates to bring you in as his guest.If nobody is there on your dates, you could still approach somebody entering the lounge and ask, if he could bring you in as his guest...

Might be a good idea vice versa as well, always a pain to trade for CO Club passes, if you want to use a Prez. Club beside the ones at EWR...