With Source-Connect and Reaper combined, it is possible to record both your microphone and the person you are connected to while on a session. In order to do so:

1. In Reaper, click Track > Insert New Track twice in order to add two tracks:
2. Name the tracks. You can do so by clicking the black bar on the track.
3. On the guest track, click "FX", then select the VST > Source-Connect Link plugin and add it to your track.
4. Record arm the guest track by clicking the red record button on the track.  Your track will look like the following one:
5. Right click the guest track and select Record: output > Record: output (Mono)
   Also, change the input to “Input: None”:
   
6. Insert a third audio track and name it "Playback".
7. At the bottom of the Reaper screen, click on the Guest track "Route" button.
8. Add a new receive and select the Playback track. 
   
9. Change the type of Receive to Pre FX. 
   
10. Record arm the “My Track” track. Also, at the bottom of the Reaper screen, click on the My Track "Route" button.  
    
11. Add a new send and select the Guest track. Also, change the type of Receive to Pre FX. 
    
12. In Source-Connect, set the Input and Output to Source-Link plugin: 1 
    

You will now be able to record your own mic and the person you are connected with through Source-Connect. 

The end result should look similar to the one below: