That Would work to kept from rattling. I would rather not JB weld them and want to just yank them out and use a heat wrap. But I suppose that should wait as I do intend to put in a header next spring at the Texas Auto Madness location on The figure 8 tour next June..
I have cut washers from aluminum flashing for reattaching various heat shields in the past; have used bits of cans too, but they don't last as long.
I can't remember if the Smart's shield is steel or aluminum, but use an appropriate material to reduce corrosion.