Buy a cheap wallet, stick a few receipts in it mabey movie ticket stubs (ask friends for some romcom guff rather than something like saw), piece of paper in it that says "if found please call xxxxxxx" and then find a worn picture of an old lady and stick that in.
Run past her in the morning and look like you are late for something, just before you pass her drop the wallet and if she calls out just ignore her. Wait for the call, when she calls you sound really grateful and releaved and explain that its the only picture you have of your gran who meant the world to you but died a few months ago. Ask if you can buy her a cup of coffee as a thankyou and bamn your in.
If she doesnt call that night then next morning look sad and pretend to look for wallet as you are walking, if she gives it to you then put on the grateful act again and ask if you can reward her with a cup of coffee.
If she doesnt call or mention wallet as you pass then she is only interested in money and as your wallet didnt have any she isnt interested in you and your better off without her.
The only downside of the plan is if your gran isnt dead then she cant attend the wedding or ever meet her