Update :
I suggested the client to open another gmail account and transfer emails by years to the new account, But then I saw that it's not that easy to transfer a group of manually selected emails and that you need to create a filter and that the filter doesn't show all the emails from a specific perios of time so :
1. I downloaded thunderbird portable
2. I configured the gmail IMAP (but only incoming server - So I won't delete something or ruin folder structure)
3. I split all of him emails into quarters on the gmail via browser (about 1500 emails in a quarter)
4. In settings-labels I marked only my folders to be synced via IMAP (Although the inbox is non UN-tickable).
5. started the download process

Whats annoying is that it downloads the inbox and i can not unsunscribe to it and it's quite big (6.2GB......)
Anyway I cross my fingers and hope it'll finish the syncing in the next few days and then I can present to this client all his emails untill the end of 2012 in a portable version