After going twice to that area with intents of doing the full Marmotte loop, I think that realistically doing it solo is just way too difficult if you do Alpe d"huez at the end (at least it would be no fun…it was all I could do to keep my cranks turning at 60 RPM at 8 kph at the Galibier summit).
The Fri-Sun trip with Fri Alpe d"Huez fresh TT, Sat Marmotte Loop minus Alpe d’Huez and Sunday on Les Deux Alpes and time permitting a climb up Col d’ornon before “heading home” is an ideal usage of time and “real mortal legs” (and even then it is a killer). Doing the Marmotte with thousands of others cyclists to draft off would make a huge diff, although I am not sure that I would want to rocket down the backside of Col de Fer with guys with sketchy descending skills. The 20 something K climb to Col de Fer is not particularly steep so if you start with 8000 riders, there will still be a ton of riders around. By the Telegraphe mini descent to Valloire, and the Galibier descent to the shoulder of Lauteret, the road should be pretty well “clear and stretched out”.
I love this area for riding. This is one set of climbs that every cyclists should do in their career only because of the proximity of numerous climbs with TdF pedigree, not to mention the astounding scenery and challenge.