You can do it on the bow, by hand or serving jig, but it ain't gonna be tight enough unless you increase the tension on the string as previously stated. In the off chance that you can wrap the serving SUPER tight with the string on the bow, you will likely cause the string to rotate while wrapping, which isn't good for peep stability. Also, you will have to use smaller diameter serving than normal because the string is a larger diameter when it isn't under tension and the serving won't be stretched as tight either, making the served area a larger diameter than it was when properly served under tension. Anyway, good luck, serving on the bow works in a pinch if you have the room to do it, but it isn't ideal.
Some bows, usually those with a higher brace height, are easier to serve on the bow because there is simply more room to spin the jig, but the problems stated above are still applicable.