Predecessor with Calendar Days on One Item

When invoicing, we use a NET30 policy where the payment is due in 30 calendar days. The remainder of our project timeline functions in working days (Monday - Friday). I want the "receive payment" step (line 31) in our timeline to be dependent on the "send invoice" step (line 62) and to appear in the tasks when the invoice is due.

Right now, in the predecessors column, the "receive payment" step reads "31FS + 30d" - but this isn't giving me an accurate date because it's 30 working days after the "send invoice" step when I want 30 calendar days. I don't want to change the project settings to include Saturday and Sunday as working days, because that will throw off the rest of the timeline. How can I get this one predecessor to count calendar days instead of working days?