Oh man, that's ugly... I sure hope the program is better made than it's written.
Here is what I would do (note this is outside the ports system so clean up could be nasty... keep the cpio file around so you know what belongs to this).
rpm2cpio keepass.rpm > keepass.cpio
tar xcf /path/to/keepass.cpio
tar czpf - * | ( cd /compat/linux/usr/ ; tar xvzpf - )
Of course, you need other stuff here as well... like the Qt4 libraries... which I don't know if they're available. It make take some work getting them installed. Although those wouldn't be this backwards. The Qt4 libraries are available on the site... but you'll need to install them outside of the FreeBSD system as well... and that's not something I've ever tried doing.
If you must use this program, good luck. But there have to be other options out there.