Good morning @humbrachtplumbin.
Thanks for being a part of the Quickbooks Community.
At this time, there isn't a way to insert a line between existing items. The workaround you've found to drag a blank line from the bottom of the invoice will be your best solution. To add, if you want to give your customers an option to pay online, you can do so by activating the Payments feature. Feel free to read this article for more details.
Please let me know if you have additional questions on invoicing or anything about QuickBooks Online. I'm happy to help. Take care!