When we enable you the module, go to Settings - Profit and and choose a specific margin for a "Fixed group: Virtual Strikethrough Prices".

Click on "Add rule"

Adjust the setting according to your needs and save the setting. Please keep in your mind that the global margin can't be than the virtual price. Otherwise, it won't show because the virtual price is lower than the current price. 
After that you will have virtual strikethrough prices on your shop. If you want to display a custom label in front of the price, write us.