I was still a long way off this by the time I had completed all the special jobs required to unlock all the districts and the specific achievements, so I eventually found a way to boost this for myself by doing the following:
Go to Special Jobs and accept The Northridge Philharmonic (you don't need any of the vehicles with required functions as we won't be doing any work at all here.)
Skip through the introductory dialog.
Fast-travel to the Steelworks in Northridge and enter.
Change the filter to 'Task Only' if you haven't done so already.
You should see only one item (Steel Beams, vertical)
Change amount to 4 and select 'Deliver to Construction Site'.
Back out and this will complete the task and finish Stage #1.
Skip Stages #2 and #3
Fast-travel to the Building Materials Supplier in Northridge and enter.
With your filter set to 'Task Only', you should see three items.
Buy 1 x Cable Drum, Large - Deliver to Construction Site.
Buy 4 x Pallet of Concrete Bags - Deliver to Construction Site.
Buy 2 x Pallet of Roofing - Deliver to Construction Site.
Back out and fast-travel to the Construction Site in Northridge.
This will complete the task and finish Stage #4.
This gave us 11 objects delivered, which is over 2% per run. Repeat until you finally get 500 objects.
Obviously, someone is bound to find a much better alternative, so by no means do I consider this a definitive solution, but for me, this was by far the easiest way without having to grind out jobs.