I don't think you can share the JSP. One possibility is to copy/paste it. I know copy/paste isn't great, but the alternative isn't great either. An alternative is to read the JSP into memory from a jar and have a servlet return the contents. Or write it to a temporary location or something. I don't think either of these alternatives is a good one.
We have a module in source control for common libraries and files. We check in the common code there, label it with a tag that links it to the other projects and set up the dependent project's build process to get a copy and put it where it needs to be. This way, we don't have to worry about which project has the "correct" version or have to make sure to update one file when we update the other. If the files do diverge down the road, we can simply fork the file in source control and maintain the two versions in the same place.