Upvote:8
Plan B makes the best sense considering it allows more time between applications and also is for a more important event, i.e. your graduation. Additionally he will have more time (hopefully) to improve his financial/stability status.
For my graduation here in the USA I invited my brother, stepmother, and uncle who had all previously been denied US visas and they were all issued. Some say it is because I attended a prestigious university, however I also believe and have anecdotal evidence that graduations have greater weight with consular officers than ordinary visits.
In my case my school office of student services prepared the invitations. That's the only thing sent from here. They carried along their own bank statements. Like you noted, nothing is guaranteed however I believe the chances are better that way.