What is an alternative to invoke_waiting?

[amol]

I was reading the channel_tests and I do have somewhat similar usecase as that of the tests which are calling invoke_waiting, where I initiate the channel by doing a send and at the same I want to be part part of "pipeline" somwhere in the middle and once I receive the result I want to return it to my caller.

tie(r, s) = channel(...)
...
auto middleMan // a receiver somewhere between "r" and "s"
..

s("start");

// once received at middleMan 
return dataReceivedAtMiddleMan;

How should I design this to make it less blocking to my caller?