Phil, what happened to the app?
Update for everyone... The app is "Real-Time Cart Hold" and it's available through the app store now at https://apps.shopify.com/carthold
I just release version 2 this evening.
Instead of the above email, I can now, and always, be reached at firstname.lastname@example.org
It's coming along great. If the process of getting it added to the app store doesn't hold it up, it will be released by the end of the month. I'll post everywhere letting people know.
Please email me at email@example.com if you have specific questions unique to you, otherwise here is perfect because of the knowledge that gets shared.
I'm EXTREMELY excited to get this to store owner that have absolutely needed a solution for this for quite some time.