When I've done it, the sealant usually holds the gasket in place pretty well. The sewing thread idea is pretty neat though, I never thought of that before.
My tip: Although it's not necessary, I find it much easier to change the water pump with the radiator removed. To remove, it requires removing only two bolts, two hoses, and two tranny cooler lines (if you have an automatic transmission). You'll have the coolant drained anyway, and removing the rad will give you that much more clearance and wiggle room. And room to fit in your socket and extensions, and your hands/arms.
Other tip: torque the bolts that secure the water pump progressively and gradually...not all at once.
The hardest part is removing the fan, I agree with that--all fan clutch removal tools suck, for lack of a better word. The tranny cooler lines can be a tough if you choose to remove the radiator. Sometimes they are on there tight.
