Apps Dialing a custom number once call picked up

[Rabbit Mobile]

I am working on an app that picks up a call, and in the dial pad during the active call, it enters a number previously saved or copied. First, I would like to know if this is even possible. Second, I have been thinking of some ideas, but I have no idea how wild they may be as I am relatively new to Android and have little idea about its limitations:

1. Store a number in the clipboard, and have some way to click paste in the active call screen which will simply paste the number into the dialer
2. Take each digit in the number stored in the clipboard, and programatically press the keys on the phone pad which the user would otherwise touch
3. Open the incoming call in my own application which can answer the call and has the capability to paste/add numbers in the dialer
4. Override one of the keys on the numpad that pops up in a call (say a long press on the # key), and reprogram it to perform the function I want (so instead of backspacing, it would enter the saved number)

Are any of these at all possible (why or why not)? Or can you suggest any other way to accomplish what I want? Thanks, much obliged.