InfoPath Dev

I found this post http://www.bizsupportonline.net/infopath2003/auto-format-time-on-lostfocus.htm that explains how to let the user type in 0730 and have it format to 7:30. My question is (not sure if its possible), if the field could accept 730 and format it to 7:30. I have tried working around with the example I had but its just not working. I am really wanting to know this becuase the users I dont think will get 0730 and will enter 730 instead. So, I want to help as much as possible to make it easier for entry.

I suppose you could try putting a rule on the field and if the field is only 3 characters long, add a zero to the beginning of the string.... may be worth a try. Mind you, I haven't thought out all the possible implications of this....