I know this is to be done by creating a .contract file in /usr/share/contractor.
For example, one like this will add a menu option to open a folder as root.
[Contractor Entry]
Name=Open folder as root
Icon=gksu-root-terminal
Description=Open folder as root
MimeType=inode;application/x-sh;application/x-executable;
Exec=gksudo pantheon-files -d %U
Gettext-Domain=pantheon-files
How to adjust such a contractor file for the 'make executable' option? What about a 'Run' option for the executable files?