Just added multi-page search and j/k page scrolling to Mu PDF via github mupdf-users. I figure everyone wants a fast lightweight PDF reader. ;)
I set up the github to be read/write for everyone, so that you can hack in support for your feature, just make it so that users have to enable your feature via an environment variable, i.e. without any feature environment variables defined, it should work just like a stock copy of Mu PDF.