Use the 'old' Mail Merge Helper - or at least the old Merge part of it.
Tools > Customize > Commands tab
Under Categories, scroll down and select All Commands
Under Commands on the right scroll down and ..
The MailMerge Helper is called "MailMergeHelper"
The Merge command is called "MailMerge"
Click and drag either or both of these to a toolbar of your choice.
Close the dialog
The Mail Merge Helper is as it was before.
The Merge can be used instead of clicking option 5 (or 6) in the new mail
merge task pane to preview the results (or clicking one of the icons on the
mail merge toolbar) and it still has the option to suppress blank lines.