I wonder how far along you are.... mainly because I am running #8 now.. and I have had troubles with the one-battle per day in a long while. As a matter of fact, they are currently 3 encounters into a 15 encounter 'day'
We just finished #4 The Mad King's Banquet, and the group has teleported to Ostalin on their way to the Monastery in #5. This one will have some single combat days, but I will try to minimize or eliminate those as much as possible.
I may try to set up a set of linked encounters leading up to a suitable BBEG, rather than having the confrontation as a single scary fight. The problem I see with doing that is that you wind up going from one fight to the next, spending much of the session in combat with no roleplaying and investigation breaks between.
As an aside, I deliberately avoided reintroducing "Rope Trick" back into the game, as they did in WotBS #4. That spell was the most egregious offender in the 15 minute adventuring day, and needed to be pruned from the game. Adding it back in as a plot device just because it was used in the original 3.5 version was a poorly thought out decision.
Thngs I have done to speed up losses of healing surges has been modified skill challenges {search "lethal obsideon" here for more} and I have ensured the group has motivation to keep moving...
Terrain hazards are one way to do it, although I don't want to make it too frustrating or require too much bookkeeping.
I also agree with the 'day = scene' idea above and have looked at earning an extended rest as a skill challenge {that paying gold at an inn can auto succeed}..but hadn't gone that route yet.
It is a tempting model since it allows the adventure to unfold at whatever pace makes sense without making combats easier than they should be because of going nova all the time. I like the idea of the skill challenge. It could involve choosing a defensible campsite, figuring out where to place guards, and banking the fire so it doesn't attract unwelcome attention. The Inn is safe, hence automatic success. This doesn't work as well if they are staying in a safe place such as an inn or manor house for most of the adventure. I doubt my group would be on board with disallowing an extended rest when they sleep because of what is happening in the story. If it works in the dungeon, it works in the town. We are too far into the game to change it.
I will just have to see that at least some days have multiple fights, and others have one really tough fight where it's go nova or die. The upcoming mods will make that easier I think.