@cliqueradar – Sadly not. I took a look at the Google docs, and the existing plugin code. I had hoped it was a case of moving some stuff around to make it work. Alas not.
The invisible Captcha requires JavaScript to be triggered at the time the form is submitted to populate a Captcha field. This is then processes as it is in the existing plugin.
I don’t know enough about Mailster’s architecture to know if there’s a hook to trigger a JavaScript function on submit. I haven’t had a chance to dig any deeper, although I’d love to find a solution as the ReCaptcha design (even the compact version) is awful on newsletter forms, and I’m pretty sure it’s costing me subscribers. Removing it opens me up to way more spam than I need, so it’s a necessary evil right now.
@everpress – Do you know if there’s a hook for triggering a JavaScript function on submit of a Mailster form? Furthermore, is there a set of developer docs available for Mailster than you know about?