You can steam it using a garment steamer. Be careful, though, as it will wilt the gumpaste so you need to do it gently.
We have a product in the UK called PME glaze spray which is a confectioners glaze in an aerosol can. It gives a very good shine and you can add even more coats for even more shine.
I spray a bit of pam on my hands thin gently rub it all over. I used this technique on the TN cake. I've heard you can use any shortening, bu his way allows me to use a very thin amount.