I would pay the rent and then just do a meander with real thread all over it. Even the best water soluble thread has to be run at a much slower speed than quilting thread and if it is a finicky longarm--it might not like it at all and you will have spent your rental & learning time fighting with thread that may never work properly. If the longarm is stitch regulated and tension adjusted for the thread--the quilt will look fine when it is finished. Don't expect a masterpiece and I think you'll be pleased with the end result. If it were me--I think I would just make up a large practice sandwich--muslin or cheap yardage--and just doodle all over it. Take it off the frame and cut it up for placemats, potholders, dog beds, etc.