Hi Shutterspeed,
I'm busy with the same sort of thing. It would be really helpful if you could use the helper object's axis.
There are some ways of working around this to create a usable result.
Method one is to map the rotation in the xyz axis. So you'd have multiple rotation animations working at the same time. The path won't be perfect, but you'll end up where you need to.
The other method would be to adjust the original axis of the moving object. Because you can use that axis! You can either model it that way, or you can add the object you wish to move to a group. Then you rotate the group to get the axis you want. Rotate the original object back, and then put the animation on the group instead of the object. You can then use the helper object for the center of rotation, but you are using the axis of the group.
I attached an animation of the result of the second method. I hope that helps.