You could sleep low, climb high, on that extra day before your climb, to help acclimatize.
The Meysan Lakes trail is near the Portal. I haven't done it but I hear it is very tough. And beautiful. Might be a bit beefy for a relaxation day.
A more relaxing option may be to drive up to Horseshoe Meadows that day and do a day hike from the Cottonwood Pass trailhead (e.g. Chicken Spring Lake, not a long hike) or the Cottonwood Lakes Trailhead (e.g. out to Cottonwood Lakes basin, where you get a great view of another 14er that is fun to climb...Mt. Langley). The hike out to the basin and back is not all that scenic (pretty woods) but the basin itself is beautiful, though probably run you 12 miles RT, though without a lot of elevation gain. There are also other loop hikes out of the Horseshoe Meadows area. Getting up high for a day will really help.
