It would work, but with some caveats. The small uberlight weighs 6 oz with an R-value of 2.0. My truck reflectix type sunshade measures 27.5″x 55″ , weighs 9.7 oz with an unknown R-value – but let’s assign a value of 2.0 also – and it certainly could be cut down to save weight. So what you end up with is a pad system that is not only heavier but also with a possible lower R-value than a small xlite pad (8 oz, 4.2 R).
This reckoning is only approximate , of course, but bear in mind that the Uberlite is not known for durability, but perhaps a reflectix ground pad is just the ticket to protect it from puncture and extend its comfort range!
Happy trails!