You can do it using the older 'shell' context entry approach. From the command line type:
REG ADD "HKCU\Software\Classes\Directory\shell\Mythicsoft Search...\command" /t REG_SZ /d "\"C:\Program Files\Mythicsoft\Agent Ransack\AgentRansack.exe\" -d \"%v\""
This has the effect of:
Create a new key:
For the default value for the key 'command' put the command line to the program, e.g.
"C:\Program Files\Mythicsoft\Agent Ransack\AgentRansack.exe" -d "%v"
So you should end up with something like:
Now when you bring up the context menu on a folder you'll see 'Mythicsoft Search...' as one of the options.
You can replace the text "Mythicsoft Search..." on the key name with whatever text you'd like to appear in the context menu, e.g. "Agent Ransack..."