I suspect a strong feel of disbelief in your words Tom
But anyhow I convinced myself to (re)write the answer :
Increase your speed by diving slightly at 5m/s. Once your reach 500+ (usually somewhere btw 520/540) level your nose and keep your trajectory straight with the utmost of attention. Your oil&glycol rads shld be nearly fully closed (at high speed the amount of airflow would be enough to cool your eng).
And Taaada ... Th's it
Your speed will stabilize at 500 and then will very slightly decrease to 480/490.
Note that with a very shallow descent (what was authorized by international authorities for high speed record) you can keep 500 IAS deck (with something like 50m/min descent (150ft/min)