As orca says and I will add further to, the ships that ask for assistance are giving you a mission that can only be completed by boarding the ship. It is not hardcoded into the engine, and giving them energy in any other way (which I doubt is possible) will not make a difference, since all the game cares about is the ShipGoal, which is set to rescue, and will not recognise you giving the trader energy. (Well, that's as far as I know anyway)
Edit: In fact the ShipGoal is set to Rescue rather than board as I wrote the first time...
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(This message has been edited by Ephialtes (edited 08-10-2004).)