Let clients select to run in mixing mode. This should allow them to select a maximum amount of risk in bitcoins. Clients in this mode send coins back and forth for blind signatures which can be redeemed for the bitcoins sent. If clients select small amounts of risk, they will not risk losing much  because they will only part with so many coins at a time for blind signatures. There is already work done and being done on mixing systems, but I see no reason why it can not be built directly into the network, for clients who want to participate. This would add noise to the transactions, and maybe some way to work it out for very strong unlinkability and little risk of participation. Then coins can mix in the background for long periods of time.