Place wood block behind portal. Place lava in front of portal. Wait.
On second thought maybe begging is not that undignified after all...
That sounds like a sucky random method for lighting a portal...
But of course this would work; Until Greg in all his wisdom realized transporting lava in an iron bucket is just silly, because after all lava is so hot it melts through most metals. He'd then makes it so you need a tungsteel (Tungsten has a really high melting point) bucket to transport lava and this bucket will not shield you from the heat. While it's in your inventory you'd either set on fire randomly or suffer heat stroke which will be nausea and slow or both. Then to add to the "challenge" the lava will eventually cool down turning in to a plain old obsidian block if it does not reach it's destination (destroying the bucket).
Ohh and even if you get the lava to the destination the bucket is only a one time use.