I usually either find a reason to get rid of that character for that session. Unless it doesn't work (they're locked in a dungeon), and unless the player ticked me off by not giving advance notice or missing for several weeks in a row.
In that case, I run the character myself.
...
And it GREATLY reduces absenteeism.
Ex: "Hang on, guys," Aldamar shouts, "I'll lure the Iron Golem toward me to distract it while the rest of you sneak past!" He then wildshapes into a wolverine and begins humping the Iron Golem's leg.
Ex: Sendant volunteers to cast Commune as many times as necessary to figure out the riddle. "The XP cost is a small price to pay," he says boldly. "No matter how much it takes, I won't rest until I've solved that mystery." He casts Commune. "Hey, is this my deity? It is? I've never done this before, am I doing this right? Great. Can I ask you about the riddle of the gargoyle statue? Do you know the one I'm talking about? Okay, yeah, about this "stone becomes water" line, do you know what that means? Gryff thinks it's ice, but he always thinks of weird stuff, doesn't he? No? Are you sure? Wait, was that no, he doesn't think of weird stuff, or no, you aren't sure, or no, it's not ice? Am I running out of questions? Dang. Hold on, I'll cast it again."
Ex: "Trap?" Gryffid scoffs. "Bah, we dwarves know how to deal with traps. You WHACK 'em!" He boldly strides past the Arly before Arly can disarm the trap, and... (roll) takes 47 points of electrical damage. "Hah!" he laughs, patting down his charred clothing. "Take more'n that to slow down ol' Gryff. Nah, don't heal me, it just makes me blood tingle."
-Tacky