As we don't know how quickly the maintainer will be able to produce a new extension that works with the updated Perl version, why not build one yourself?
There is a build script
available that was most likely used for the existing extension. After downloading it one would have have to (at the very least) address the issues of changed tools and dependencies, e.g. via
sed -i 's#squashfs-tools-4\.0#squashfs-tools-4.x#' buildirssi
sed -i 's#openssl-0\.9\.8#openssl-1.0.0#' buildirssi
followed by the execution of the build script (e.g. via sudo sh buildirssi
All going well one should end up with a new set of extensions, that could be used for some local testing. Please note, that there will be more changes required to create a "proper" new extension (e.g. to provide a working solution for icons etc., and an update of the info file), but I guess this is at least a start.