The ipk's install Lua its libs in /usr/local (about 1MB I believe). It would take some effort to configure those to run in another location... But you can uninstall the ipks easily on the commandline:
ipkg remove lua5.1-iliad lgob-iliad
It's quite safe. You CAN unpack the ipks (they ar 'ar' archives with a tgz inside), and copy the files yourself to /usr/local, but that is certainly more error prone than using ipkg...