I'm a little rusty but I think part of the problem is there is nothing 'above a job' in jobops like a project. For example, in Epicor you can create a project, and then create as many jobs broken down into phases and link them to the project.
If you do decide to pursue this, for you and the clients sanity (and to avoid lawyers) I strongly recommend you do a paid proof of concept with some percentage refund if they move forward with the project. You don't want to sign a $100k+ project to find 35 to 50% into it, you hit an unexpected roadblock and have a disaster on your hands.
If for some reason you hit a brick wall, let me know and maybe we can work out some joint deal using Epicor.