Build a smart contract (NOT TOKEN)

We are a wallet service provider (centralized) and so we want all the ERC20 tokens deposited by our users to be moved to our master wallet. This is not possible in direct way, because user's wallet do not have ETH balance to pay for the fees. So we cannot move the token form their wallet even if we have the PK for it. So we have found a solution here: https://ethereum.stackexchange.com/questions/64686/collecting-erc20-balances-from-multiple-addresses

Bid only if you understand what we want, rubbish and copy paste will be directly flushed down.