Fuel pump & delivery hose TE449

I need to replace the fuel hose from the fuel pump to the injector, simple enough. However the bike is full of fuel (and by full, i mean about 20L as i have a Bianchi Prata subframe tank). The fuel taps on both the main and the smaller "pump tank" are seized so i dont have an easy way of stopping the fuel going anywhere.

My question is this: will fuel gravity feed through the fuel pump if i disconnect the outlet house or will most of the fuel stay in the tank and I'll just get a dribble from within the hose.

hell, just pinch the hose between the main tank and the header tank (and maybe the header vent too). Use needle-nose vise grips with tape on 'em.