How to promote to Samurai with Boost

[iMemphis]

You have to first assign a base class. Then use a Modern Vocation book to change the retainer to another job once it is adequately leveled.

I get that, but I don't have a "base" class. My main is a 78 samurai that was boosted as well. So is the only way to assign my retainer a Samurai, I have to go back and level a older class? The website is quite misleading then. It just says it will boost to 70, as long as my character is 70 or higher also. Well, my character is a 70 samurai. I don't have any of those base classes.