my ds2 is a seriously bad bolter, but he has just come to the realisation now that he has to be in the stroller at the shops. often when i first get there, i will take the kids to the small indoor playground they have set up there, grab myself a coffee and let the 2 of them run wild in the play area for 10 mins. then i strap ds2 in and ds1 walks along next to the pram. i only have limited time that this works for though so i try to quickly get it all done and get out!
best of luck with it, it's a horrible situation to deal with xo