Hi DL
You can actually achieve this using XSitePro... I know, I've done it

It's a little convoluted, but here's what you do:
1. Grab the embed script for a new Twitter account (for said restaurant, club, etc.)
2. Set up a "Tweet by mail" account and point it at said account
3. At this point, I actually added a form on my web page which (using a PHP mail script) pushed the message from the form through to the Twitter account via Tweet by Mail, and appeared on the page instantly.
4. The Tweet by Mail requires a specific "sent from" address, so while you could mail yourself, the restaurant customers might have to send to an address which itself then forwards the message on...
Hope this helps!
Rich
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