Having multiple fields in the same position

I've got an option set, and depending on what is picked, a different field is shown beneath the option set. So, I added all the possible fields, but the problem is that they are under one another - so if I pick, for example, the last thing from the option set, there is a big space between the option set control and the relevant field.

Is there any way to display the relevant field in the same position no matter what is chosen from the option set - ie. directly underneath the option set?

Or is the only option to change the label? The fields that are displayed are of different types - text box, check box etc., so it might be very messy to change that too, if indeed it is even possible!

Thanks.