Chanspy - one way call bridge


I am creating a special app based on asterisk and I need to separate rx/tx strams in two different channels in order to eliminate possible audio loops & feedback.

I was thinking of using ChanSpy / whisper functionality to do that, but I can’t get it to work. Perhaps someone could tell me what the likely problem is … My setup is:

I have two SIP channels, extensions 103 and 502. Both extensions have established calls to different meetme conferences.
I have these extensions set up:

[spy] exten => 7502,1,ChanSpy(SIP/502,q) exten => 7103,1,ChanSpy(SIP/103,Wq)
The I try to originate call, which would spy on one channel (502) and whisper the stream into the other one (103)

Call is established, I get notice about starting to spy, but no sound gets through… is that a bug or am I doing something wrong ? Would it help to break that in two calls and join the with meetme conference ? Or is there any easier way to do what I need ? Perhaps inside meetme ?