Parameterization or Script Elements in Offers

I am looking for a way to collect information form a texbox and block the ability to accept offer based on validation of information entered.

I have been successful with embedding scripts and parameterized fixlets when taking action, but haven’t gotten very far trying to implement in an offer.

At the very least I’m trying to figure out if I can override a function like the example below for ontakeaction but the the equivalent offer function. I’m not having any luck discovering those functions though.

document.body.ontakeaction = function (event) {
return false;
}

Ideally I’d also be able to pass the information from the textbox into the action as a parameter not necessarily so it can be used in the action script, but just so I have the ability to view the parameters value entered from the action.