AFAIK there's no function to do that atm. You might need to build your own script to do that (and make sure others accept it). It could work but the coding part is not easy.
But, is there any reason why you give coins to Bob? If there's a possibility of him running away with money, you can either sent your funds directly to Alice, or use a multi-sig 2-of-3.
I need BOB to make an assessment of worth of ALICE services.
Ok, so I will need to have a smart contract that BOB can only tell pre allocated amounts to Alice to shift.
I am quite interested in ALICE having the freedom to move coins after that as then ALICE is incentivised to do their best to earn the coins