I think this has been asked several times before and no, there is no way.
If I remember correctly UT always needs one thing in your loadout which is the same, everyone has a knife.
Some peole also suggested that you should only be able to access the knife through a special button, so that you can't scroll to it and lose important seconds, I don't know why they didn't implement this, because this is possible it is used in StrikeForce this way.