IOS – Reject incoming call while on waiting

If I get a call while I'm busy with another call (call waiting, normal call, not FaceTime), can I reject that incoming call?

I'm using an iPhone 5 running iOS 8.2.

I didn't try anything till now, and I don't want to turn the call waiting off. I want to decide whether to accept or reject the incoming call while I'm on another call.

The screen that appears when I receive another call has only three options:

1. Hold the current call and ANSWER the coming one
2. Hang up the current call and ANSWER the coming one
3. Reply with a message to the caller (of the new call)
   none of the options actually allows me to REJECT the incoming new call and keep the current one going