If you have tried everything, and just cannot figure out what the kernel is asking kerneld to do, there is a way of seeing the requests that kerneld receives, and hence to figure out what should go into /etc/conf.modules: The kdstat utility.
This nifty little program comes with the modules-package, but it is not compiled or installed by default. To build it, go to the directory where you have the kerneld sources and type make kdstat. Then, to make kerneld display information about what it is doing, run kdstat debug and kerneld will start spewing messages on the console about what it is doing. If you then try and run the command that you want to use, you will see the kerneld requests; these can be put into /etc/conf.modules and aliased to the module needed to get the job done.
To turn off the debugging, run /sbin/kdstat nodebug.