You could split the animation so that (say) the up/down and any rotation animation is done in the motion control settings for the pencil clip and the horizontal movement was done using the 'transform' plugin. Once you've created the initial loop, let's say just an up and down movement (two position keyframes) using the motion controls. Now copy these two keyframes and then paste them (a few frames later) to repeat the movement. Do this for as long as you want the up/down movement to happen.
Now apply the 'transform' effect to the same clip and use this to move the pencil across the screen. You only need a start and end keyframe for this. The linked video below shows what this would look like (it's only a very quick and dirty animation).
You could then use a wipe or animated mask on your 'drawn' image to reveal the picture as the pencil moves across the screen.
It won't necessarily look totally convincing but if the movement is fast you might get away with it.
Many 'manual' keyframes would be much more precise and effective if your pencil needs to correctly follow the drawing but honestly I'd be doing that in After Effects.