Hi Terri,
I teach business English in Japan for a major manufacturer. "Business English" is an extremely broad category and students don �t often realize what it is they need to focus on beyond "doing business in English".
Since you mentioned his promotion depends on improving his English, I would first recommend learning how his English will be tested to gauge his worthiness of promotion. If it is a test of sorts (like the TOEIC test that is loved by companies here in Japan), I would spend some of the class time focusing on improving his test score. Tests as such require specific test-taking skills and often do not correlate directly with an actual speaking level.
To this point as well, I would recommend performing a detailed needs analysis with him in order to pinpoint the range of vocabulary he will need in his job. (ie Graphic Design vocabulary will differ largely from that needed by an accountant).
From there, you could then use that range of vocabulary/content to focus on things like presentation skills, email writing, meeting facilitation, negotiating, etc.
If there is no "test" to speak of, and his skills will be rated by general conversational ability, it sounds like you are on the right track with starting with general English first. I would personally continue down this path for a period before tackling business materials.
During his general English studies however, I would recommend that you focus on his ability to speak politely and "intelligently" (using less colloquial terms). Simple examples would include changing typically used word and phrases to more business-like ones:
too - as well
so - as a result / therefore
for example - for instance
want to - would like
need - require
little by little - gradually
etc.
What I often tell my students is that business English is just general English spoken much more politely :)
Finally, in terms of class content, I would recommend finding a suitable text series as opposed to grabbing various things from the internet. The only reason being that your preparation time will be far less and there will be a more focused goal (i.e. finishing the text). Textbooks also often include nice appendices with vocabulary lists, grammar points, listening scripts, etc. which come in handy.
FYI My favorite text for pre-intermediate level learners is a series called "Get Ready for Business". I find that many Biz Eng. texts series (especially those by Oxford) are far more difficult than the level they claim to be - especially the listening exercises. This series IMO hits the level right on the nose. But, then again, I find teachers� opinions on textbooks to be VERY subjective so of course you need to find one that suits your teaching style as much as it suits the student�s level.
http://www.macmillanenglish.com/courses/get-ready-for-business/
Good luck,
Lee