This is something that has never come up before but I just can't imagine it working or how you would design it. The old ball on a string is much cheaper.

Here's my thought on designing an inexpensive mirror trick

The big question is though, do you think the existing sensor circuit can carry the beam an additional round trip across the width of the door in a letter "Z"?

Let me explain the "Z", we have two existing sensors (S1 & S2). Place S1 at the bottom of the door where it should be (this is also the bottom right end of the "Z"), place S2 higher up aligned to protect the car (this is also the top left end of the "Z"), purchase two more sensor brackets and place them at each bend on the "Z", now attach a mirror to each of the two purchased brackets and align them to reflect the beam from S1 to S2.

Do you see what I'm saying, kind of difficult without pictures, let me know. Maybe I should patent this?

Thanks
Selvan

Interesting idea. I'm not sure the infrared beam is strong enough to travel that far. The difficult part will be aligning the mirrors. If you decide to try it I hope you will let us know how you make out.