Using Auto-responder Emails & Attachments

Is there a workaround to adding a file to an auto-reply email (upon form fill) that includes a simple .ics file?

I’m using Unbounce for event-specific landing pages. I’d like to reply to anyone who completes the conversion (fills out form, submits) with the typical “thank you, you’re registered” type of email but attach a calendar file to that so they can easily add the event to their calendar.

Am I missing something? The native integration doesn’t seem to allow this and building a Zap to do it with Zapier has proven fruitless, too.

Thanks in advance!

--Craig