Top Tether anchor point in Fabia 03 reg

Hi, I have a fabia 03 reg and I want to install an isofix group 1 car seat in it for my son. The seat has a top tether which needs anchoring behind the seat and my fabia doesn't have the anchor point for doing this. The new fabia does, and my husbands 08 octavia also has them. I have read online that it's possible to retro fit an anchor, does anyone know anything about this or had it done before? Will be ringing my local dealer but they're shut til monday now and if I can't do it the seat needs to go back so would rather know asap. Thanks, Lynne