The following is assuming you are a Costo member and are paying either by cash, debit or Amex card only:
Enter the Costco branch of your choosing,
Head to the tyre bay,
Choose which tyres you'd like,
Exit the tyre bay and purchase a hot dog and a slice of pizza at the cafe,
Return to the tyre bay to find your tyres fitted and either your wheels still perfect or horrendously damaged depending on your chosen branch (I can recommend both the Manchester and Chester fitters as ok with mine on 4 visits so far but I have heard horror stories from other branches..)
Pay for your tyres or argue about the wheel damage,
Drive home with £150 of wholesale goods you didn't need but felt compelled to buy, I still have 60 pots of chicken noodles from my last visit btw..