Select user and retrieve meta

I have the registration add on and will have users register for subscriber level accounts with all their information.

I then am creating forms that only ad admin will have access to. How can I have a dropdown that will show the last name, first name of all registered users (alphabetized) for the admin to choose who they're filling it out for.

Upon selecting the user, I then want some meta fields to be populated with what is currently in the user meta fields. This is so if the user changes those values later, this form entry has what was there when the form was submitted.

What's the best way of doing this?

Example:

Dropdown field of users last name, first name.
Once one is selected the fields for weight, waist size, and height will lookup those meta values from the selected user and enter them into read only single text line fields.

This is easy to do if the person filling out the form is needing those meta fields from their own user. But in this case it's an admin filling out the forms and needs to select the user and have it populate with that selected users information.