If anyone stumbles upon this, I was able to make this happen using a paid Zapier account. I have a field on the Deal that will trigger a Zap when specific options are selected. I select “new deal property change” to select the field on the Deal, then “filter by zapier” to specify the option selected, then “create line item” to create the line item, then “associate line item” so that the item appears on the deal. I had to repeat the “create line item” and “associate line item” for each product I want to add, but was able to do that all within the same zap with the paid account.