If you haven't yet check out this API widget I seriously recommend it. Dynamic Personalised images by uploading a Photoshop file which then plugs into your Campaign Monitor fields!
I heart Daisy API so bad - thanks for sharing this! It was an excellent find, especially in the lead up to the holidays. We've also got a blog post on it here.
Except I've now ran out of custom fields to use for them. Is there any way to increase the custom fields limit?
Not at present, I'm sorry to say - happy to add your vote for more than 20 custom fields, though! I'll certainly let you know if it's something we add - in the interim, you'll have to remove custom fields created by Daisy API once you're done with them.