I would go back and check over your seperation agreement, I find it hard to believe that a lawyer would of missed his pension during the equalization stage. The pension is generally the bigest thing on the list. You would of been entitled to 50% of it for the years you were married unless you took something else of equal value....maybe like a paid for home.
If I were in his boots, and I am, I would look at the buy-out, determine how much more child support this would generate, then I would go to a bank and open a RESP for the kids in that exact amount and drop the remainder into my RRSP. I would get the tax break on both accounts and you would be hard pressed to find a judge who would force cash up front when considering you are still receiving your regular child support payment.
And he can also petition the courts to reduce his payments on retirement. If for example you change the rate every Jul, after he receives his tax assesment, he can motion to the courts to change it early to reflect his retirement date. Generally most don't do this because we avoid the courts as much as possible but if you are going after his buy out, what the hell, he'll be there anyway.
After re-reading your post, I'm left with one question: How old are your kids that are receiving child support?