It is possible to create a jenkins job that when run:
- scans git for any newly created repo.
- creates a new jenkins job for new repos.
This is achieved using the the following plugin:
https://wiki.jenkins-ci.org/display/JENKINS/Job+DSL+Plugin
as well as writing some groovy script.
This jenkins job can then be run as an hourly cron job, or manually, as and when needed.
Also see:
https://github.com/jenkinsci/job-dsl-plugin/wiki/Tutorial---Using-the-Jenkins-Job-DSL
https://wiki.jenkins-ci.org/display/JENKINS/Jenkins+CLI