jQuery.post() Using serialized form data, and custom object in submission

When doing ajax stuff with jQuery you can pass your data along to the server in two key ways:

1. Use an object like

   {
    firstname:'blah',
    lastname: 'derp'
   }
   

2. Use a string like &firstname=blah&lastname=derp

(1) Arises naturally when you're passing in values programmatically.

(2) Arises naturally when you've got input fields.

My problem: it doesn't look like you can combine them, i.e.

jQuery.extend({
 firstname:'blah',
 lastname:'derp'
},jQuery('form.some-form').serialize());

And it's been nagging me for a while.

Truthfully I think they just need an objectified version of the serialize method that just gives you a json representation.