No we don't have a workpaper options but do provide a Web Link feature to link documents to your workpapers. Refer to Creating a Web Link.
You can attach Xero Workpapers to FYI documents using the Web Link feature.
FYI does not integrate with HowNow but HowNow is an Add-in to the Excel ribbon and works with the FYI Add-in so you can create Web Links.