The only way to avoid the stamp duty would be to purchase the property in your wife's name (as she IS a 1st time buyer). The mortgage would then need to arranged in joint names (assuming you need both salaries to qualify for the amount required). You would need the lender to accept the application with both on the mortgage, but just your wife on the title.
If you wifes salary is sufficient to qualify for the mortgage required, then she could purchase the house, and draw the mortgage. This would avoid the stamp duty as she is a classed as a 1st time buyer.