Microsoft DHCP server with option 252 (proxy pac)

That is correct.  The only other suggestion I can provide if you go wtih the GPO option is to place a shortcut on the user's desktop to disable the proxy setting via a change in the registry. 

Enable and Disable Proxy Settings via Shortcut
http://www.anitkb.com/2011/07/enable-and-disable-proxy-settings.html

I havent really used option 252 in DHCP for configuring proxy settings.  however, here are some articles that may be of use:

"Automatically Detect Settings" Does Not Work if You Configure DHCP Option 252
http://support.microsoft.com/kb/307502

Automatic Discovery for Firewall and Web Proxy Clients
http://technet.microsoft.com/en-us/library/cc713344.aspx

Create an option 252 entry in DHCP
http://technet.microsoft.com/en-us/library/bb794881.aspx

AutoCAD Hang - AutoCAD Application has stopped working

AutoCAD 2015 LT, sometime hang up. 

Log Name:      Application

Source:        Application Hang

Date:          31/1/2020 17:57:11

Event ID:      1002

Task Category: (101)

Level:         Error

Keywords:      ClassicLog Name:      Application

Source:        Application Hang

Date:          31/1/2020 17:57:11

Event ID:      1002

Task Category: (101)

Level:         Error

Keywords:      Classic

Open task manager and find the "WSCommCntr1.exe" process and kill it. (This
is your autocad Communication Center) Then see if you can open up another
session. This problem has popped up a bit. Do a search for wscommcntr1 and
find some more info. Just have time right now to get you on the right
track.