Consider each year all citizens were sent a number of coins which could be spent into the agency that they would like and they could adjust their spending preference as follows:
It might be possible for people to buy/sell their preferences (haven't given that much thought)
As it would be on a public ledger, the citizens should actually be able to trace how each of their coins are spent. Employees and vendors would exchange the coins they would receive (banks would need to accept them) with the government issuing fiat to the banks. The coins would then be programmed to return to the original wallets on an annual basis.
This would mean that a citizen might allocate their spending preferences once and it then be handled automatically after that or each year would modify it in time to affect the budgets for the succeeding year.
This would take part of the decision making process out of the hands of the few.