Ok, after thinking about it, there are two methods, and IT DEPENDS ON WHICH CHARACTER YOU ARE PLAYING AS YOUR MAIN. Knowledge about your play style is key.
Simple method. If you play the Crusader as your main.
Goto Always On, right click on the Activate Repeater mapped key, select Create Alternate HotKey.
Select the "Activate Repeater - Alternate", set the Hotkey to a key you will HOLD DOWN while this will disable the repeater.
Set the "Hold any Keystroke Actions" to Off
Set the Execute a Step to "pressed OR released"
Basically this will, depending on the state of the Repeater to begin with (which is generally always on when playing D3), toggle it's status while you are holding it down.
More complex method, if you switch your main between characters, or you do not always play with the repeater on.
Use the Mapped Key Wizard (under the Wizards Menu).
Select Combat key map (because this is a fighting thing), Click Next
Select Broadcasting Toggler, click Next
Name your toggle (doesn't matter, it's so you know what it is)
Set the Hotkey you will HOLD DOWN with your fingers while this is in effect.
Set the Toggle when the hotkey is "pressed OR released"
Broadcast FROM any of these windows "Window:Current" <--- this means that this toggle will send the click from the window that you are on
Broadcast TO any of these windows "Slot 1 (Crusader)" <--- this means that this toggle will send the click to only this character
Tick the Block buttons from current window
Hit Finish
Now, if you always play with Broadcasting ON, you will need to edit the toggle to make sure it is still on when you let go of the toggle.
Goto the Mapped Key you just created.
Drill down to step 2
The second action, will set Key repeat Off, Mouse repeat Off. You should set these to ON
If you don't always play with Broadcasting ON, it gets a bit more tricky, but
Goto the Mapped Key you just created.
Drill down to step 1
Right click on Actions, add a new Key Map Action -> Mapped Key Step Action
In target, set Window: All w/Current
Key Map , select Always On
Mapped Key select Activate Repeater
Step Adjustment, Add 1
In Step 2
delete the existing actions
Right click Actions, select Key Map Actions -> Do a Mapped Key Action
Target is Window:Current
Key Map , select Always On
Mapped Key select Activate Repeater
Both of these options affect the WHOLE BROADCASTING state, but as they rely on you holding one button and clicking the mouse, I figure when you let go of the button it goes back to normal so you probably wont have other actions going on, while you are clicking. And if you do, set them up as Mapped Keys so they still work!