yeah +forward wont work because its not a nnormal cvar command. (Uses pfnAddCommand) which uses the input keys stuff on the client. (Have a look at keyDown on the sdk..) I don't think you can access that stuff though a server
oh yea.. for the gravity stuff you can maybe add your own code to not update the velocity at certain points if the player is falling (not on ground) etc.
and you could also try PlayerPostThink on the player after setting the buttons, can't remember if pre-think resets the buttons or something, but since its done on the client I would guess not.