So, try adding the layer to a web map using its URL, and instead of the regular service URL, use the URL for the individual layer, "/MapServer/0" or whatever the layer index happens to be.
When you do that, it treats the added layer like a Feature Service, and may give you different capabilities. However, you'll lose any "fancy" symbology or labeling that the Map Image happened to use. But maybe that's more tolerable than publishing a new service for one map.
- Josh Carlson
Kendall County GIS