Got a link or any info on the restrictions?
I'm taking my bike home on the same route in January. I plan to wash it pretty damn thoroughly so that there is not an ounce of dirt anywhere near it. Same goes for my shoes and armour 'cause they will check that too.
I'll also be declaring it to customs not trying to sneak through the 'nothing to declare' route. They are more likely to be forgiving if you front up and say that you have a bike, that you are aware that they need to have a look at it and offer it for their inspection rather than be sneaky.
You could consider paying a shop to wash it and get them to write a quick letter stating that they have cleaned it. I don't know if that will help anything, I wasn't planning on it myself.
Leaving the tyres behind is a good suggestion. I will be ditching the ones off mine except for a new nevegal that's only been ridden once so by the time I clean it it will look brand new.