There is only one way past Iceblood. You need to have a stacked defense there though. Some up front towards where the roads come together just past IB tower and some a little further back by Tower Point to catch the stragglers that make it through.
We can hold off the Alliance indefinitely at our gate if we're willing to do it. I've played in some Horde AV premades where we have a strat called "Sweaty Armpits." Basically, we let the Alliance take all of our towers and wait for them at our base. We then hold them off at our gate and whittle them down until they run out of reinforcements. Yeah... it takes quite a while, but it is doable... even with as few as 20 in the premade.
The bridge is a great chokepoint as well, but it's not insurmountable. Horde has to make a concerted group push across the bridge and through the Alliance that are fighting at the end of it. Too often, Horde stops on the bridge and doesn't push through. In order to succeed on the bridge, they need to rush as a group straight through to the aid station and cap it to keep the Alliance from rezzing back there.