How do I template a command with a binding?

[jim-alexander]

I want to be able to click <leader>fr which will enter the command: :%s//<cursor_here>/g but not actually enter it until I actually enter the word I want to Find and Replace.

This is what I have so far but I can't find any way after a long time trawling through the docs / forums / issues, to acheive this:

// Enters command mode with the cursor after the : (what you'd expect)
    { "before": ["leader", "f", "r"], "after": [":"] }

// Doesn't work
  { "before": ["leader", "f", "r"], "after": [":%s///g<Left><Left>"] }
  { "before": ["leader", "f", "r"], "after": [":", "%s///g<Left><Left>"] }

Here are some keywords that I searched for when hunting this issue elsewhere in hopes it helps someone else:
Find and replace binding, find and replace keymap, template a command for execution, Create command with cursor at position.

[jim-alexander]

Guess its not possible.