How about a 50% surtax on anything earned after leaving the federal government, above whatever the federal salary was. Example, leave a $300K job at the White House, take a $1M job with Goldman-Sachs, and pay a $350K surtax. Such surtax to be in effect for ten (10) years.
Now, I'm mostly after elected and appointed positions only, not the hired rank-and-file, but they don't completely escape either. Those worthy folks being paid a salary in the upper 20% percentile of taxpayers would have their 50% surtax only kick in for the difference at 20% above their public-sector salary, and would be limited to only(?) 5 years. All those above the 20% income level take the big 10-year bite with the rest.
And while we're at it, let's take the pain another step further and say that any salaries paid to such former government officials aren’t tax-deductible for corporations while the surtax is in effect. See? There's a private-sector penalty, too.
Some enterprising budget hawk (from either party) should add this concept to a spending bill and watch the fur fly.