Alas, apart from the same options you listed, deleting old jobs, reducing copy retention and running a data-aging job, I have not found any other way to reclaim space on the DDB partition/volume, much less to speed-up the process, and none of these are ideal since you are effectively reducing the restore-points etc.
Just looked again and I have found a setting in the Control Panel > Media Management > Service Configuration tab labelled, "DDB disk space chek interval in minutes" which has a value of "1440" which equates to once-a-day (24 hours). Theoretically you could lower this to "720" to run twice-a-day, though I would only do this after checking with support on whether this is supported, or a bad idea due to the potential overhead it may incur to the Commcell.
There is also a "Deduplication" tab in Media Management Control Panel dialog, but I do not know that any of the settings in this tab would be of use for what you want.
The other option aligned to this is to adjust the built-in Data Aging Schedule Policy to run more frequently to deal with DDB and disk library space issues, but again, I do not know that this is a good practice, let alone sustainable or as effective as lowering backup copy retention or manually deleting old jobs and then waiting for the regular 12 PM data-aging job to run just once.
Just saw there is also the built-in "System created DDB Space Reclammation schedule policy" in the Schedule Policies which appears to be the most simple/relevant option, however, I am not entirely sure this Schedule Policy is tied to "garbage collection" or pruning etc. I presume that if you are on SP 14> and ran a compaction of the DDB to make it compatible with the new DDB that supports garbage collection, then this schedule may be relevant, but support would likely be able to confirm this (we currently do not have this schedule policy enabled since we have not yet had a chance to compact all our DDB engines try it out.