I have a client who was Trading as for a few years then became incorporated Jan 2015, however they only started using a company bank account May 2015 I was going to set up a bank account in VT for Trading as from Jan to May as the transactions are business related but not sure of the rules in the cross over of trading as and ltd company?
You will need two bank accounts on VT - one for the actual new business account, and one to use as a dummy, to get the transactions from the sole trader account, into VT.
All you need to do is post business items per the sole trader account, and then write off any balance to the directors account, once thats completed.