GET form field that is not editable

Hi
Thanks for providing an excellent and lightweight form plugin!
I use the form for subscriptions to events, and I pass GET variables from several different event pages to the form page.
I put the event name and the date in two GET variables, and I need these to be shown in the form when the users enters additional info like name, email, phone number.
I can pass the GET variables to the correct form field. No problem. But I need the form field to be un-editable, because the user already chose event and date – and should not be able to edit these in the subscription form.
I cannot use the other GET form field, because it is invisible to the user.
Is this possible?
Thanks in advance ??
Cheers
Johnny

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