How do I make a subform with a transparant background?

I want the subform to be an "overlay" to the main form
where only the text boxes on the subform are visible.

The reason for this is that I have a form with many
controls. I refresh the data every 5 seconds. For some of
the values this is not often enough, so I would like to
refresh some of them every second. I pictured I could then
just put my transparent subform on top of the "5-second
values" - and then just refresh some more often.