The Java-based AppleCommander disk image handling application has been updated to add support for Apple GEOS files.  According to the comp.sys.apple2 post by David Schmidt:

AppleCommander command line support has been added to properly place cc65-produced GEOS files on ProDOS images.  John Matthews has posted the 1.3.5.11 build in the AC download page:
https://sites.google.com/site/drjohnbmatthews/applecommander

This pico-release adds the -geos argument.  Given a GEOS file in Oliver’s CONVERT format:
http://wiki.cc65.org/doku.php?id=cc65:apple2:geosconvertformat

AC can be invoked like so to place that file on a disk image:

java ac.jar -geos disk.po < file.cvt

Since the CONVERT format includes a filename and other ProDOS atributes as part of the specification, there’s no need to add anything more on the command line.  If you like to do things by hand, though, you can achieve the same result this way:

java ac.jar -p disk.po foo GEO < file.cvt

Again, since the CONVERT spec includes all of the ProDOS attributes, the filename (foo) and filetype (GEO/0x82) are actually overwritten and/or ignored as part of the process.  But the presence of GEO as filetype is the thing that triggers the special GEOS handling.

John B Matthews announced today that the latest version of the Apple II disk image management application, AppleCommander is now available.  This version, “features refinements by David Schmidt to allow writing Pascal TEXT files on DOS ordered disk images.”  Visit the AppleCommander Sourceforge page to check in on the latest project developments and to download version 1.3.5.10.