Vacuum full of parent without partitions possible?

Hello,

I have a table that used to contain all data. 

because it grew too big I added a partition trigger a long time ago and since than all new data was added to small partitions. By now all data in the original parent table has become obsolete and was deleted, however the disk space cannot be reclaimed without a vacuum full. The problem is, a vacuum full of only the parent table should be instantaneous since it contains no rows, but because the vacuum full triggers a vacuum of all partitions too, it's not possible to do this while the application is running (a vacuum full of all partitions easily takes over an hour during which the table is locked.) 

Is there some workaround for this? 

Thanks,

Jan