Unit conversion smart tags.

Hello, I'm typing some very long text in MS Word and periodically I have to type in different values for speeds, distances, etc.
The problem is that I have to type in both British units (mph, yards, feet, inches, etc) and their correspondent values in Metric system in parentheses.
For example:

... 3 feet 6 inches (1.07 m)...
... 55 mph (24.59 m/s)...

etc.

Because there are so many such values in the text and there is a unit conversion smart tag which recognizes them and offers conversion air, I wonder if I can automate the process, say, I typed in 55 mph and (24.59 m/s) would be added immediately after that?

I've never programmed smart-tags in Office, so I wonder if anyone could help me with this?

I could have done this with .Net and RegEx I guess, but I think that's an overkill.