Just kidding.
I figured this out earlier today while I was messing around with bipeds and globals. Go into reflexives, select bipd, then mp_bipd, then bitmasks, then the second set. Turn on flying. Then go into floats (still mp_bipd) and change the following:
Bank Angle: 3
Bank Apply Time: .25
Bank Decay Time: .25
Pitch Ratio: 3
Max Velocity: 3
Acceleration: .25
Deceleration: .25
Angular Velocity Max: 3
Angular Acceleration Max: 3
Crouching Velocity Modifier: 2 (optional, causes crouch to boost your speed)
This mod is partially CSS. People without the mod can still play, but they will experience lag and jumpiness.
If this is a fairly well known trick, then I'm sorry for posting it. I just thought it was neat. If not, I hope you enjoy it