[eluser]Otemu[/eluser]
Hi,
Here some options for you:
Find a new host or maybe you can ask if there can enable it
Extend and override classes that use base64_decode within Codeigniter
Replace core classes with your own
I ran a seach using the word base64_decode, I only see it listed in the Encrypt library and Xmlrpc library so maybe you can just extend these helpers and put your own functionality there.
Hope that helps