Amazon.com are the only videogame retailer I know that lets you pre-pay customs. However, they are very fickle about what exactly they will or won't ship outside of the US (PS Vita -- totally fine, Blu-Rays -- totally fine, Nintendo game -- NO) and it only affects things sold directly by Amazon.
I've not looked into weather it is possible to arrange things direct with HM Customs (as in hold all packages sent to me until I have paid duty).
I'm of the understanding things from HK and China are far more likely to be checked and take far longer, too.
Same thing happened to me. 3DS games arrived quickly and without issue in my mailbox, WiiU games (DVD case sized) take FOREVER and I'm expecting to head to the customs office again next week or so since my NSLU still hasn't arrived (preordered, shipped on release day). It's pretty annoying.
Someone on hotukdeals just received an £11 invoice (£8 Royal Mail BS+actual tax).
To add some salt to this wound, Amazon has it for £25 now...this reminds me of Pokemon Silver, my first import (back when FedEx sold videogames) and I end up getting the game a week later than a friend who got gold (the price they paid was cheaper without the customs, too).
I think my verdict is avoid Wow HD for anything over £15.
£8 flat admin charge, is that UK only?
Yes, but your countries postal service (or courier who sends package) may have a similar fee.
Play-Asia have
Radiant Historia (DS) for just 17,92 euros.
27p over the safe limit for UK using the PA currency conversion...(but it matters not, it is down to the $ on the day customs inspect it)