If you give the player an outfit that increases the no-jump zone to larger than the system, you have effectively disabled the J-key, until such a time as you rescind the outfit.

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M A R T I N • T U R N E R
(url="http://"http://www.AmbrosiaSW.com/cgi-bin/vftp/show.pl?product=evo&category;=plugins&display;=downloads&file;=FrozenHeart104.sit.bin")Frozen Heart(/url)
(url="http://"http://www.AmbrosiaSW.com/cgi-bin/vftp/show.pl?product=evo&category;=plugins&display;=downloads&file;=FemmeFatale.sea.bin")Femme Fatale(/url)
(url="http://"http://www.ambrosiasw.com/cgi-bin/vftp/dl-redirect.pl?path=evo/plugins&file;=Frozen Heart - the No.hqx")Frozen Heart - the Novel(/url)