exactly. I was thinking of handling this in pre-run and post-run scripts as a workaround: Configure backup job to run very frequently (every 30 minutes or every hour). Then with a pre-run script, check connectivity and see if a run was completed today. In case no connectivity or in case a job was already completed today, return non-zero to abort the job. On every successful run, the post-run could create a file that the pre-run checks for existence.
Too bad these kind of scripts depend on the platform.