A lot of ways

But you should plan long before you need it. It is very hard to ask someone who barely knows you to write a letter.

(1) When you go to conferences, try to catch the big ones in your field and impress them with your something (your boss, your capability, etc). Follow up your conversation with email after you come back.

(2) Your boss may help you to land some letters. Try to ask him/her whether this is possible. Just ask plainly.

(3) Look around yourself. If you find your colleagues have some accolade to boast, maybe you can give him a makeup before he gives you one. After all, most CIS officers only have high school diploma.