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\""
More information
This has the effect of:
Create a new key:
HKEY_CURRENT_USER\Software\Classes\Directory\shell\Mythicsoft Search...\command
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.
Note:
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..."