Passing page url into a custom field via the Press-This bookmarklet

Here’s my situation. I want to use a modified version of the WordPress Press This bookmarklet to pass the current page URL to a custom field on my post. In this case, let’s say my custom field is linked_list_url.

I’m guessing there are four pieces to this:

• Add a custom input field to the page generated by the bookmarklet
• Grab the URL of the page the bookmarklet was used on and store it
• Pass the stored URL to the custom input field
• Pass the contents of the custom input field to WordPress, setting it as the key for the custom field

I’ve modified the bookmarklet to have a custom input field and it’s pulling the URL off of the page and passing it to the input box, but when I submit the bookmarklet, nothing is passed to WordPress.

Here’s my press-this custom bookmarklet: http://pastebin.com/UjNkpNrE

Specifically: Once I have the URL passed to the custom input field in the bookmarklet, how should I go about having the contents of that field passed to WordPress into the custom field linked_list_url?