For anyone looking for a solution, you can use personalization tokens as variables: {{contact.firstname}}
So when linking a piece of text in your email, you could for instance do this in the URL: www.domain.com/?first_name={{contact.firstname}}
I’ve only tested this in a test email but it seems to work. For a full reference on these variables, see the ‘Add personalization to a coded template’ section here: Use personalization tokens