Hi Xavier,

Yes that is possible – there are two ways to achieve that:

Deploy the assembly as local:

1.       Add the custom assembly name in the referenced assemblies:
-          Go Editor Tab
-          Select Build / Referenced Assemblies from the menu
-          Add the custom dll – for example if named CustomDllName.dll the entry should be “[AppDir]\CustomDllName.dll”
                                                                                                                    
2.       Copy the CustomDllName.dll to the following locations:
-          For BIDS 2008 copy the custom assembly to C:\Program Files (x86)\Microsoft Visual Studio 9.0\Common7\IDE\PrivateAssemblies
-          For SQL Server copy the custom assembly to C:\Program Files\Microsoft SQL Server\MSRS10_50.MSSQLSERVER\Reporting Services\ReportServer\bin

Deploy the assembly in GAC (assembly must have a strong name (signed)):

1.       Add the custom assembly name in the referenced assemblies:
-          Go Editor Tab
-          Select Build / Referenced Assemblies from the menu
-          Add the custom dll – for example if named CustomDllName.dll the entry should be “CustomDllName.dll”
2.       Copy the CustomDllName.dll to GAC.

Hope this helps – let us know if you meet any problems or have any questions.