If we want to provide continous liquidity to the Pass tokens, we can upgrade the ERC20 smart contract and add an automatic price-discovery based on a reserve in Eth in the smart contract. We could organize a new Pass tokens CO (Coin Offering) in order to have a sufficient initial reserve in Eth.
Each time a delivery business will buy tokens for the payment of deposits when taking parcels, it will automatically increase the token price. The same for a trader who wants to speculate. There will not be any liquidity issue because the seller will be the smart contract itself. The same in case of sale. See the Bancor protocol about smart tokens.