Hi ellenclary: I remember seeing your name in the rock creek canyon discussion.
The answer to your question is yes, it can be done. It is not however the easiest thing to do and would require an extra 3-4 hours or so, some of it cross country. If you leave your backpacks up at Iceberg lake it is way easier to just return to Iceberg lake the same way, down the MR.
However that being said, what you are proposing would end up being a hike of exploration. For sure it would be different then the usual experience. Some do this so that they can go to Mt. Muir and experience trail crest, the 97 switchbacks and trail camp.
From the top of Whitney down over trail crest to trail camp is about 4.7 miles with an elevation loss of about 2450 feet or so. Trail camp is a little lower the Iceberg lake, by about 550, so you will have to go back up hill some. From Trail Camp you head north (to the west of Wotan's Throne) over a series of boulder fields. From the top looking down the boulder look very flat. But up close they are perhaps a few hundred feet high. On the south side the pinacle ridge is very gradual, even though it is steep on the north side. Before you get to the ridge you turn east until you get to the pinacle pass. You can tell where it is because it is the low point, with a pinnacle point sticking up on the west side.
The south approach to the pinnacle pass is quite easy climbing. On the north side it is steep class three climbing for the top 50-100 feet or so.
Once over the pass it would take another 45 minutes or so to walk across the scree field and go back to Iceberg lake. You need to go back up hill 200-400 feet or so, depending on how high you stay after you come over the pass.
I have a few pictures of the pinnacle pass, which we came over twice from Thor peak on our way to Iceberg lake.
http://client.webshots.com/album/215977132YyrhmI