I know this may be an old request and an answer may no longer be needed by you.
But I think we should all try to answer any questions we can and make this forum more useful to anyone in the future who may have the same question.
The answer is Yes you can.
Select Options
Then click on the Order tab
You'll see two relevant lines for your query.
Order Number: if you set a number here that's the first number your invoices will start at.
And
Number Prefix (optional): If you set a number here all your invoices will start with that number.
Hope this helps you if you haven't already figured it out.