If you go through customs you can sew the seeds up in your clothes or put them loosely in your pocket or luggage.
I have been through custums a few times and the way I see they operate they cant see the forest for the trees.
With lace up shoes you can put them under where the laces go with a few weed seeds and other plant matter even if they look that hard and see something they will just think it was settled in there from walking in the woods or fields.
Worth