I'll be on that route in late December as well. In Penitentes we typically cross the highway and hike up to the top of the ski hill to begin our acclimatization. I believe you can reach over 10,000' here.
At base camp (Plaza Argentina, 13,800') we usually climb part way up to Camp one, rest there for a while to aid acclimatization and return to base camp. There is also some good bouldering outside base camp towards the English Glacier I believe. Just follow the river outside of base camp up stream and you should be able to see the huge boulder around the bend.
At Camp 1 (16,300') you can attempt to summit Ameghino (19,225') on the right from Ameghino Col. For more info you could contact fellow SPer William Marler who has been on this mountain almost every year since the late 80s and check out his Ameghino page on SP. You could also try contacting fellow SPer juh33 who climbed this peak last season.