Yes you could, if they wanted to they could do a back calculation. Based on the reading you are at the time they took the blood, they work out what you were likely to be at the time of the accident.
Obviously if they do this you would need to get your own expert to see if the reading they come up with is accurate, but it is likely they would come to a similar conclusion unless the time scale is very short between crash and the taking of the blood (which you have stated it was not).
That all said, if they have already said what they are charging you with it is unlikely they would add the drink driving charge. The dangerous driving charge is serious enough already and they will be introducing the evidence of the blood test which was just under, so it is likely they would just proceed with one charge.
My best advice is to get a lawyer on the case straight away.
kind regards
Martin.