Excellent question and something I hadn't tried with an ultralight.
I inductively coupled my Youloop to my R-108 this morning. The standard 1 meter Youloop diameter shows about a 3 dB gain over the stock internal ferrite bar on 1 KW WGVA in Geneva, NY on 1240 KHz, so it shows promise.
It's possible to approximately double the size of the Youloop using the 6 ft. feed coax that comes with it, by joining the two 3 ft. lengths of coax together with a coupling and using them as one half and the 6 ft. section as the other half of the loop. Doing so resulted in about a 6 dB gain on the same station (over the internal ferrite bar).
Better results should be had with a little amplification using a preamp.
I was surprised seeing any gain at all. These small single turned coaxial loops don't output much signal.