Here are some instructions to trick Messenger into thinking it's using the 2009 version, when actually it's 8.5. 
Note: I haven't tested it, so I can't confirm it works. Some details may not be exactly right.
1. Firstly, exit Messenger so it is not running.
1. Download 
ResHacker.
2. Once open, go to File > 
Open > C:\Program Files\Windows Live\Messenger\
msnmsgr.exe.
3. On the left, select the 
Version Info folder, then 
1, then 
1033.
4. In the main panel, scroll down to where it says: 
code:
VALUE "ProductVersion", "8.5.xxx"
The x's represent the version you have.
5. Change the version number to the latest Messenger version, example: 
14.0.8089.0726
6. Click the 
Compile Script button.
7. Then go to File > 
Save.
8. Close ResHacker. Run Messenger.
If you have problems, you may need to run 
ResHacker.exe as administrator (
instructions).