I've run into this also, usually with light fixtures. My electrical supplier carries type SA wire which is silicone insulated with a fiberglass jacket, rated 200C for dry locations. It is a little pricey, so I too use a j-box nearby to make the transition. Most wirenuts I've encountered are rated for the 105 degree temperature.

Few things are harder to put up with than the annoyance of a good example.