I don't think that there is a set-in-stone method of creating a portmanteau Stevo, so workaholic seems perfectly fine since it is easily recognizable for what it describes and is easy to say.

Portmanteau, I believe, are generally created so that they can slip off of the tongue. The hard-to-pronounce ones, like infotainment, are more often seen in print since nobody really wants to be sputtering over a word - you look more foolish than "in the know" about the new word.