I realized that it is extremely easy to build searchhandlers for KHelpcenter. I have always wanted to use beagle for searching in KHelpcenter, so I quickly made a searchhandler in python. Screenshot below. To use it, put these files in the right places, chmod khc_beagle.py to make it executable and restart KHelpcenter. This only searches the manpage index for now and can be easily extended to search docbook. And of course you have to remove /usr/share/apps/khelpcenter/searchhandlers/man.desktop. I would submit it to KDE bugzilla but I dont know if this works with KDE4 version of KHelpcenter.