Invitation Inserts for Online Rsvps - Minted

I am ordering invitations from Minted, and also using their wedding website. I decided to go with online RSVPs instead of using response cards. However, I still need to put an insert in the envelope directing guests to RSVP online. I did not want to put this information in the invitation itself, as it would look too cluttered. The problem is that there is no existing product like this in the invitation suite. I contacted customer service and they suggested that I order business cards from the same independent designer, so that they can use the same design element and fonts that are in my invitations. They said I can explain what I'm looking for in the "design requests" section. The purpose of ordering business cards would just be to get the right sized card. I think that technically, I could order the reception cards that are included in the invitation suite and just ask them to edit the text, but those are pretty large for what I want. I could also do the same thing with the response cards, but those are large as well and they come with envelopes that I don't need. Overall, I think "business cards" are a good idea and they are cheaper than ordering response cards or reception inserts. But since so many people seem to be doing online RSVPs these days, I was surprised that Minted doesn't offer the kind of printed insert I was looking for. Just curious... what is everyone else doing?