Bechstein's and Brown Long-eared can be difficult without the benefit of bat researchers - if you know any, or if there is a bat group near you, get involved.
Dormice: which ones? Hazel Dormice are difficult but not impossible in the right habitat: look for winter nests in hazel stools. Find out what signs on chewed hazel nuts indicate dormice as opposed to mice or voles in order to establish where they are, then stake places out with passive night vision or use camera traps to localise them. Edible Dormice if present are a piece of cake, they are very vocal and can easily be spotlighted with red light (they shoot away from white light at high speed).
You are correct that Bank Voles are very forthcoming compared to other voles! Small mammal traps (Shermans or, for preference, Longworths) are the best bet. Other than that, baiting with piles of high energy food can work, but the trick is not to lose them to other feeding animals (or those pesky birds...) If you can find small mammal runs then baiting those, or the entrances to nests, can work. Drystone walls can hide a thousand rodents and voles will have trimmed the vegetation round their lairs.
If you find out any tricks for seeing polecats, tell me. I've only had one or two scamper across roads on night drives in habitat since the fabulous College Lake litter. Badgers are easier. Their setts are generally pretty obvious. Canal cuttings and steep river valleys with sandy or earth banks to dig in are a good place to start, my nearest canal has Badger setts in every cutting.
Pine Martens are really difficult unless you know someone who has them visiting a feeder or similar. Having said that, they can be attracted to feeders fairly easily if they are in the area. Eggs, peanuts, raisins, (jam and peanut butter are being recommended against by "experts" though I'm not sure of their reasoning). Foxes and Badgers will also take this largesse so the trick is to put it where only Pine Martens are likely to get to it.
Hope some of this helps!
John