I recently got some advice on this front from and advisor who's been doing this stuff for years and has read hundreds (thousands?) of LORs. She said that action must always be first and foremost. A good LOR is more verbs than adjectives. It's easy to say "Seattlegirl has a superb intellect and a caring soul" but hard evidence to back that up is critical to set you apart from the crowd.
If you have some writing he's done, try to mimic the voice, or at the very least, try to shake up your own writing voice for this one. A few commas where you wouldn't ordinarily put them (or an extra parenthetical or two) can't hurt.
I would agree, but make sure that you do put in fairly strong language. It is important not to write a 'satisfactory' letter about yourself. Your letter should use some well-chose adjectives to stress the efficacy of your performance of the verbs.
I'm sorry if my first post came off as bitchy or condescending. I was not trying to disparage you - I just wanted to highlight the positive side of this opportunity. I would feel awkward writing my own LOR as well. Since your boss put you in this situation, however, he is most likely comfortable with you writing your own. I'm sure an experienced attorney will understand that you are trying to put your best foot forward and will not feel as though you are being cocky. Make sure you don't claim anything that you didn't do, but dress up the achievements you accomplished. If a certain adjective seems too strong, I'm sure he'll take it down a notch. However, if one doesn't seem strong enough, it's doubtful he'll crank it up. That is why I believe you should take advantage of praising yourself with as much charity as possible.
I'll be happy to read your LOR if you want..