You could use a workflow to sum it all up into 1 line
Just make a saved transaction search that adds your $0.30 per item/line that matches your item group. Then make it a summary search
Use that search as the source of a custom field on your sales order
Then make an Other Charge item for sale (Can be Fullfilled = ‘F’. And call it whatever you want.
Then make a workflow and use the. Create Line action on After Record Submit
In your action set the item to your custom item above, quantity is 1 and Rate is from your custom field above