Afraid I think that could only be done with some seriously long transfers; Germany is simply too big to do in one or one and a half stages from Schleswig-Holstein to the French border; Åbenrå to Hamburg all on the Autobahn is a full stage length, Bremen to Dortmund is a pan flat 240km+ on non-Autobahn traffic, then you'd have to transfer across the Ruhrgebiet to Köln to get somewhere you could reasonably get into France from - and even then, it'd be 240km by fastest route, go through Luxembourg and only touch the last 5km or so in France to finish somewhere like Thionville. I can't imagine the Danes being too keen to spend all that money on the Grand Départ then only to get a prologue or TTT and then a stage start and the first 50km or so of a flat stage. That's notwithstanding that the Köln-Thionville route would have to bypass almost all the hills en route to get to a UCI-approvable length. Afraid from Denmark, maybe one stage finish in Germany (like the 2009 Vuelta's Dutch start with stage 4 ending in Liège... but if they did that an Öresund Bridge-crossing stage finishing in Malmö would be WAY cooler) but other than that it's almost certainly going to have to be the conventional way of early rest days and transfers back to France.
A perhaps realistic scenario for a not too brutally awful few days might be:
1) København - København (prologue, preferably, but ASO would probably choose a TTT)
2) ? - Vejle (annoyingly ASO doesn't like circuits, and the one they use in the Danmark Rundt is probably too short for a TDF péloton, but a few laps on a hilly circuit here would be ideal)
3) Vejle/Herning/Horsens (somewhere like that) - Århus with a few smaller hills mid stage. Alternatively, Åbenrå - Hamburg with a few bits exposed to the wind in Schleswig-Holstein and the Waseberg
Another option ASO might consider given their current tendency would be to make the København stage a road stage, possibly circuits of the (truly awful) 2011 Worlds circuit, or doing a double-cross of the bridge to detour into Sweden just because they can, then have a short-to-mid-length TT or TTT on stage 4 after returning to France, which with a short air transfer from Hamburg or Århus to somewhere in northern France could be done in the evening of day 4 to eliminate the need for an extra or early rest day.
Most importantly, however, is that they need to learn from the 2012 Giro. That Danish start was an abomination, truly woeful and one of the worst introductions to a GT since Britain's first stage of the Tour de France, going back and forth on a closed stretch of dual carriageway back in 1974. Maybe those run-ins they chose are fine in the Danmark Rundt, with 16 teams of 8 riders, most of whom are familiar with racing in the hard fast and flat conditions of Danish racing, but for 22 teams of 9 including some climber's teams with some flyweight riders to protect, it was a recipe for disaster, and what we got was three stages of boring racing where we waited for the sprint, then didn't even get a half decent sprint because half the sprinters were sprawled out on the floor (oh, hi, Ferrari). Denmark can offer better racing than that.