Printing headers is not an ASE function - it is result set metadata. It is up to the client to determine whether to print these or not. Obviously, "dumb" clients such as isql simply offer a switch that they are either on or off.....unfortunately, there really is no mechanism for ASE to send back to the client to stop printing headers ...or to stop printing them.
One option is to turn them off and then simply use two print statements - one with header values and the other with '---------' to simulate the headers.....but then that only works if that proc is invoked in its own isql session with -b.
.....but if you want them off regardless other than then...that might work.