maybe multiple select isn't the right way to think of these...
maybe different lists is the way to go
or nested sortable lists..

looking into different options for a sortable list, preferably with multiple select options...
would be nice if click,shift-click worked to select,or.r_gc.r_pw.r_cp.r_qf.,cf.osb&fp=cb5928975d0a7e48&ix=seb&ion=1&biw=1024&bih=514

This is a nice working example, that seems simple enough
no longer maintained
(forgot about multiple select at this point though)