A hydra den is 100/100, and hydras take 33s to build, so you can easily build hydras when he pushes out and have them out in time for the attack. The battle can still be tough and pretty close, but it lets you hold the push straight-up.
The idea behind this build is to play standard:
double gas at 6:00
roach warren/evo at 6:45
@1st 100 gas, lair, 3rd/4th gas
macrohatch while lair is forming
@2nd 100 gas, ling speed
next gas: upgrades (not sure what is best; I am thinking just +1 carapace now, but I do +1melee/+1 carapace in some of the reps below, better for longer games)
Now, at lair completion, instead of spending 100/100 on roach speed, build a hydra den.
Then play normal; don't build any hydras, don't get range. Just pump lings. You should be stopping drones at 55ish and making pure lings if you suspect the push. I also like to get about 4 roaches since they add significant beef to your army. If he doesn't push, drone up, get infestation pit/upgrades/whatever you want and try to harass/shut down his 3rd with your ling/roach army, and play standard.
If he pushes out, start building hydras. Spend all your gas on hydras (4 gas) and the rest of the money on lings. If his build is clean, your hydra den may still be finishing as he pushes out. This is fine - you can still get hydras out in time.
Here are some replays vs masters toss. Note that in all these games, I build hydras AFTER he pushes out:
http://drop.sc/270235 - This is vs high masters with a 9:00 moveout on Ohana. I don't even flank.
http://drop.sc/276966 - On Cloud Kingdom, pretty normal game.
http://drop.sc/276967 - On Cloud Kingdom again. I have to pull drones, but I mop up pretty easily with reinforcements.
http://drop.sc/276964 - On Daybreak. An example of a game where I have about equal drones with his probes (I had to drone pull) after the fight, but because I'm able to resupply drones quickly and tech switch I win pretty easily.
http://drop.sc/276968 - A loss on Ohana. My hydras don't have enough of a meat shield this game because I overcommitted and didn't pull drones appropriately.
With hydras, your build still has to be very clean, and if all your ling/roach die, you HAVE to pull drones to tank for your hydras, or pull back to wait for reinforcements. Never let your hydras fight alone.
Also the typical things you should do against this build still apply: fake ling surrounds, great creep spread, flanking, etc. Still, if you engage smartly you don't have to do any of those things and you can still win.
EDIT: A typical criticism of going hydra is that he can just retreat and go colossi. However, colossi take SO long to get that you can easily transition to corruptor and max out in time, while droning and getting to 6 gas (if he goes to 2base). Here is an example:
http://drop.sc/277488 - He sees my hydra/ling army and retreats. I immediately drone and scout him. When I see the robo bay, I drop a spire and max out on roach. He pushes with 3 colossi and I crush it pretty easily. He ends up basically basetrading with me because I handle his warp prism harass really poorly, but I'm so flushed with cash that I max out and have to build a ton of spines to free up supply for corruptors. I engage horribly, especially when attacking into him, and nearly ignore his harass, don't get infestors or tech to hive, but I win because I'm miles ahead.
If he goes to 3base, it's like the game resets where you have 55 to 45 workers and slightly more tech with equal armies.