I would think that writing a line end character to the active cell would do this for you. Other than that, you can try using an event structure to capture the enter key, then programmatically get and change the active cell location. I am pretty sure I have seen examples on how to do this with ActiveX. At least the changing the active cell programmatically part.
I came across your post when looking at what is available for this in the commercial market. There is lots of options but none that do just what you want...I wanted to ask if you ended up finishing what you built. I like the idea of labview as you can customize it however you want to do what you want. Before I ask our labview guy I wanted to see where you go to. Instead of reinventing the wheel maybe be able to see what you have as a jumping off point and go from there.
Thanks for your time.