I think your issue could be resolved. I found a tool which might fulfill your requirement.
You may download a Sobolsoft Tool to merge multiple RAR files into a single file without decompressing all. Here is an excerpt from the link i found this tool from.
Unlike some other RAR tools which allow you to nest a RAR file into another, or force you to decompress the RAR files before creating a new one with all the resulting files, this effective tool from Sobolsoft simply merges existing RAR files into a new, compressed RAR file, without decompressing anything, or nesting files, and thus making it easier for you to find a specific file within a RAR container. The new resulting file will contain all those files previously included in the original containers, and following the order in which their respective files were when the merging process started.
For more about this, you may follow the link http://join-merge-combine-multiple-rar-files-in.software.informer.com/