Not the best but you could setup hourly appointments on your calendar and have a reminder setup for it to go off. If you created it on the phone you would have to setup 24 of them and have it repeat daily.
If you do it in Outlook you can probably setup it up easier and faster and then just sync it to the phone.
Again, not the best way but it will beep but not go off like an alarm over and over again.
I wanted this function as well and I just downloaded "BBClendar Free" and it works perfectly for this, better than an inexpensive digital watch!
Just go to the Advanced section, enable the hourly beep and even set which hours (mine is 8 AM - 10 PM) and what minute of each hour it beeps on. Just be sure to leave the program open when you go on standby or it won't beep.
As the App's description says, "Hourly Beep helps you to take a moment to rest in a busy day for every hour."
It would be easy for a developer to use Push so the app doesn't have to stay open. Just means they need a server side piece for peoples configurations.
Then they could send out a push and thus a sound without having to leave app open. Though I cannot see a developer paying the cost to maintain servers for an app like that.