Adding Total Deposit to Left List On Manual Remittance Screen (GESFRM)

I'm trying to add the total deposit on the left list on the Manual Remittance Screen. This value is a summation from the PAYMENTH table on the field AMTCUR and is present on the screen as "Company Total." I'm struggling with how to go about this because it's not just grabbing a single field. Is it possible to add this using an expression in the selections fields? Any recommendations are greatly appreciated.