It is more important that we know what size grips you have , first off they need to be for 1 inch bars not 7/8. Are the grips to large or to small for the throttle tube? we can't see them,we need more info!........(want to know how to mount your grips? .......I'll tell you tomorrow)

I'd use a beer can or vegy can (alum) to make a shim ,glue it around the tube using clear silicon,and a couple of 1 inch hose clamps to hold it in place until dry, then slide the grip on ,it should remain aligned.You may need to use the silicon for the grip also to keep it from twisting on the shim and ruff the surfaces with a light sanding to give it a little bite.