Speaker to microphone on-the-fly

Here is what I wanna do,I have an text-to-speech program which I would like to use on a VOIP program.The text-to-speech program only allows to output the sound to the speaker(if there is any that allow it to act as the microphone that would solve my problem,but I don't know any),I would like to take this sound output by the program and capture it on-the-fly to the microphone,so on the VOIP program the person would hear the text-to-speech program.

I really searched for a program that allows to do it,for hours,and didn't find one that worked.