Something like this, where we can use c4d render variables and use custom frame number paddings:
Second thing would be implementation of propper multi-matte setup, in octane ObjectTag we can set the objectID, but it renders in multiple colors and is not very useful if you need more than 3 high quality masks from those colors.
Cool thing could be the same workflow like in vray and redshift, for masks in post production, where you can setup multi-matte AOV swith RGB channels and each channel assign
object id number, this can be used to get more that 3 masks as pure Red, Green, Blue channels.
Only thing is, for every next 3 ID numbers you have to create new AOV, but it is very useful, because it is much more managable.