Since this should only be a last resort you could limit any recovery to accounts that have no recent logged in activity to reduce risk.

Google at least have your past IP addresses which should allow law enforcment to identify you (at least narrow the question down to a handful of people who could all be asked if they have a claim to the account unless you only ever accessed it from public networks). Doing all that detective work is not going to be cheap but right now you don't even have the option to pay for it if your online account is worth a lot to you.