The Quick Capture recording is in the device's internal memory,  and presumably it is still available there after you've inserted an SD card and entered Multitrack Recording mode. So theoretically you could playback the Quick Capture recording after having initiated the Recod function in Multitrack mode. However, I haven't tried this and the mechanics of the available menu navigation and button-pushing may not support this. You would need to find a way to get back to the Quick Capture screen and hit the Play button after initiating  the Record function in the Multitrack screen.

Other than that I can't think of a way to do it, but perhaps someone from Line 6 will provide a more definitive answer.