I faced this problem during working and I found that I have two approaches to acheive this :
 
either I ask the 3rd party developer to assign strong name to the dll or you do the following:
 
you should use Ildasm.exe tool to dissamble the *.exe or *.dll assembly to *.il and *.res (compile resource script)
you can find Ildasm.exe tool at this path on your machine C:\Program Files\Microsoft Visual Studio 8\SDK\v2.0\Bin
 
open the *.exe or *.dll assembly you want using the IL DASM and follow the images to dissamble the file
 
 
img1
 
img2
 
 
img3
 
then you reassemble the *.il file again using Ilasm.exe and passing to it the strong name you desire and here is the code
you can find Ilasm.exe tool at this location C:\WINDOWS\Microsoft.NET\Framework\[your version of asp.net] Ex. v2.0.50727
 
first you will need to create your strong name key using sn.exe tool which you will find it in this location C:\Program Files\Microsoft Visual Studio 8\SDK\v2.0\Bin
 
so to create a strong name key type in the visual studio 2005 command prompt the following sn.exe -k name_of_the _key.snk.
 
after you create the strong name key you will find in this location C:\Program Files\Microsoft Visual Studio 8\SDK\v2.0\Bin
then use the Ilasm.exe to reassemble the *.il file again by typing the following code in the visual studio 2005 command prompt Ilasm.exe filename.il /key:name_of_the_strongnamekey.snk this will generate *.exe file from the *.il
if you want to generate *.dll file you will have to add the following option /dll to the code to be like this  
Ilasm.exe filename.il /dll /key:name_of_the_strongnamekey.snk
 
refernces: