Depending on what you call "great credit", and whether or not you have any funds available to use for a down payment or closing costs, it may be possible to determine a "finish line" for you - a time in the future that, given that you follow necessary steps to improve your credit position, you could obtain a loan. A number of sellers are willing to work with buyers on options; however, you must be cautios that the transaction is structured in a manner which is good for both parties.
If you truly want to "buy", then there are opportunities, even if it takes several months or even a few years for you to close on a permanant loan.
Just be careful and refer to professionals who are knowledgable about such options so that you are protected from predatory practices.
Best of luck to you and your son.
Let me know if we can help in any way.