I propose to the government a single vehicle registration.
As the current system is set up so that every vehicle has to be registered, you can introduce an additional unique code, such as a tax number. This unique code then links all registered vehicles of the same owner. Upgrading the system to an additional unique code should not be a problem and could be introduced relatively quickly, as you already have all the details of the registered vehicle and owner. So if an owner has several registered vehicles, group them under the same owner.
Registration would still be paid for separately for each vehicle, but the toll and insurance would be uniform.
We would split into two groups:
single-track vehicles and vehicles up to a gross vehicle weight of 3500 and up to 8 seats + driver
 
Perhaps you could at least consider a pilot group, say for single-occupancy vehicles you could pass a temporary law to test the positive and negative effects of this change.