Adding new "Actions" to konqueror?

I would like to add some new actions to the "Actions"-submenu
(choice when right-clicking on file/files) to the konqueror
filebrowser.
If it's possible, it would perhaps be better suited to be placed
under
the "Compress"-submenu.

As far as I can tell, Actions are .desktop-files stored in
share/apps/konqueror/servicemenus/* (either in the global or
per-user KDE-directory), specifying a command to "Exec" and a list
of filetypes that can use (or should be excluded from) this action.

I would like to define a new actions that works a bit like the
"Compress to Folder" action in Window$; that is take a list of
files -- and/or one or more directories (though it may be better
to make seperate actions for those cases) -- and make a tar.bz2
archive of them, with the name of one of the files/folders (first
or last) with ".tar.bz2" added.

The important thing, is that I need to...
-add multiple files (and folders)
-don't have to specify a name for the archive
-don't have fumble with some dialouge (the archive is
just created without further prompting)

The built-in Actions/Archive seems to either make a seperate
archive for each file (when multiple files are selected), or
start karchiver and needs a name for the new archive.

I've made some fledgling attempts, but apparently my
..desktop-files were not valid. I couldn't find anything in the
konqueror documentation; so if anybody could point me to
a place were .desktop-files are described (especially the
various codes that are substituted for selected file(s) in
the Exec-specification), or to where I can read more about
making my own Actions for konqueror.

Using 'tar' should be sufficient. The problem is to get konqueror
to pass the list of selected files in a manner 'tar' can use (e.g.
just
filenames (not paths) and perhaps with whitespaces quoted), and
to pick a name for the archive (from the file-list).

Any ideas would be greatly appriciated, because I'm totally stuck...
-Koppe