Training - how can I get my company to pay?

Hi,
would appreciate any advice -

I want to get my company to pay for a management course that I want to do in the evenings, part-time...

The trouble is that the course is not essential for my job (though it probably is for me if I ever want to get anywhere!!)

Question is, how can I persuade my boss that it is worth it for him to pay some if not all of the cost? What benefits can I tell him he'll get?

thx