Custom mirroring

Hi, I need to set up an intermediary mirroring service between GitHub and GitLab.
I want to workaround GitLab’s native mirroring, you can find some details here Changes to refspecs are ignored after updating to 14.1 (#337340) · Issues · / GitLab · GitLab

Namely, I need to pull-mirror only the Pull Requests on the push events (via webhooks) from GitHub and instantly push-mirror them to GitLab. Usually, it’s easily done with editing the refspec. Is this possible with Gitea?