IsMouseUp is the same as Not IsMousePressed, right? Why not just use that (check the "Not" box)?
To implement Initial Only for the mouse, you could add a parameter to the mouse pointer sprite (assuming you have a mouse pointer sprite) called "WasMousePressed" and then check:
1. If IsMousePressed
2. If WasMousePressed != 1
a. WasMousePressed = 1
b. Do Stuff for intial only mouse press ...
3. Else (if IsMousePressed was false) WasMousePressed = 0