Sometimes Chilkat’s customers know more than we do — and that was certainly the case here. Thank you Michael (an accountant nonetheless) for figuring out how to use the Chilkat .NET assembly (for the 2.0 Framework) in SQL Server 2005 SSIS!
The "secret sauce" is to place the ChilkatDotNet2.dll in this directory:
(where nnnn is a version number)
and then deploy the Chilkat assembly to the .NET Global Assembly Cache (GAC), which you can do with the gacutil.exe utility.
Apparently, this is also required when using Visual Studio for Applications.