Place the main footage on track 1.
Place the cell content on track two and drag it into sync. The audio waveforms may help line that up. Then mute the cell audio if necessary (right-click to the left of the track).
Higher tracks override lower tracks, so the cell will be seen when the cursor reaches its start point and the main track will pop back on when the cell footage ends.
To dissolve into the cell click the f at the top-left of the clip and specify a duration. 