Refer to http://forums.gentoo.org/viewtopic-t-926854-highlight-.html

emerge mtpfs
layman -a poly-c
layman -S
emerge sys-fs/jmtpfs

Note media-libs/libmtp should emerge with USE(-crypt).

Then use jmtpfs mount the device:

 jmtpfs -o allow_other  /media/galaxy_nexus/