This may help?
Tick the checkbox for "Send Value to Server".
Checkbox is on the "Client-side" tab in field properties on the netwebform.
You can also add "Server-side Code" here.
eg. call a routine, and in the routine use the primaryid from the droplist to lookup your hot field.
I don't think a droplist has hot fields, but whenever the droplist changes, you can send the value to the server, run some server side code, fetch any hot fields you need, save to session values.
Hope this helps,
Alan