You can ride two up on a Sportster by changing seat and suspension and you'll be good to go. I rode two up coast to coast and back (Connecticut to San Fran) with my wife. Not for everyone but it can be done with relative comfort.
I'm 6' and about 280. My wife is about 5' 8" and, well, let's just say she's appropriately sized to match me.
Dude,
2-up coast to coast on a Sporty? I don't care what kind of seat you got, you definitely get the "Iron Booty" award. (in leiu of the word I wanted to use!! )