Skyblock Wither Help

[Frighton]

Hello there,
I have recently returned to Minecraft and am particularly enjoying the RenMX Skyblock server, however I seem to have reached a standstill; I am currently stuck on a Skyblock challenge in which I must defeat "The Wither". If anyone has reached and completed this challenge, I would love to hear from you.

To create "The Wither", the heads of three Wither Skeletons must be obtained, which in Skyblock seems almost impossible. As yet, I can see two possible ways to spawn Wither Skeletons in the Skyblock Nether;

1. Hope that in the area in which your Nether Island spawns, the seed would have ordinarily generated a Nether Fortress. This area would then have to be found by placing multiple platforms and waiting for when (and if) a Wither Skeleton spawns. (This is what I am currently working towards, but of course there are no guarantees that my area would have ordinarily generated a Nether Fortress).

2. Convert the few Mob Spawners at the top of the Nether Island into Skeleton Spawners (spawning Skeletons in the Nether will produce Wither Skeletons 80% of the time). This method is by far the most straightforward however, it requires a Skeleton Spawn egg which is not offered with the other eggs as challenge rewards and so may be unobtainable.

If anyone has any ideas or advice in getting around this problem it would be much appreciated.

Thanks, Frighton.