Hi Ming,
There is a school of thought that says "white spirit" helps, personally I wouldn't bother, it can cause hot spots in the head under combustion, you might as well put unleaded in. I like to look after my vehicles and personally think that both those solutions are a bit harsh and I wouldn't want to do that to my motor.
There is a company in Cheshire who supply an anti-gelling product that you mix with the bio in your tank. I can't think who they are at the moment but will check back in my files.
Bio-diesel is common in Germany, and is to EN Standards, and all the BMW engines will run on 100%, as will the VW/Audi diesel engines. The problem is that both companies and Land Rover have declined their warranties last year if you use bio in the UK. It is all down to the quality of the product, they can't guarrantee the stuff you put in is good as the stuff in Germany and France etc,as per my previous post.
On the continent, as you are no doubt aware, the French have a std 5% mix with their diesel. Because it's low sulphur diesel like ours, they added bio to give it back the lubricity that is now missing from diesel.
To help in winter or cold weather, I've found the easiest solution, is either to buy the anti -gelling stuff or just fill the tank half full of bio and half of std diesel. I wouldn't put "white spirit" in the thing personally.
Believe me if the bio-diesel supply you get is good stuff, get it in you won't be disappointed, its far better than standard diesel, your engine will thank you for it. It's lubrication properties are second to none its cetane values are higher than standard diesel and the emissions are a joke, there is none. If you use Millers Diesel Plus to help then Bio-Diesel does this on it's own.. Hope this helps.
There are conversions which give you a seperate tank to put std diesel in and it uses your std fuel tank to put filtered chip oil in, you have a heater system which brings the viscosity down and allows the motor to run on it when it gets warm. Works a treat but can cost a few hundred pounds. I think the company is "DieselVeg" in the midlands they have a web site which helps and the other is "journey to the neds of the earth" I think.
Personally I prefered to use the bio, it was so much simpler and CHEAPER at 85p per litre. Bear in mind I do around a thousand miles a week.
Tone