The credit card processing fee can be included in your invoices by increasing your prices a percentage slightly more than your credit card fee. Or use this formula to raise your prices the exact amount of the fee:
(price + fixed) / (1 - rate)
where price is the original price, fixed is the fixed component of the fee (ie. 0.3), and rate is the percent component of the fee (ie. 0.034).
If your agreement or contract with your customers allows you might be able to add the fee as a separate line item on the invoice so long as it applies to all payment methods equally.
Then set a discount equal to the price increase to offer your customers the original price for ACH payments. Visit the My Account page, enable the checkbox 'Discount ACH payments', and enter the discount rate.
This is the preferred practice for recovering credit card processing fees and is actually protected by legislation in 10 U.S. states: California, Colorado, Connecticut, Maryland, Massachusetts, Nevada, Oklahoma, Washington, Wisconsin and Wyoming.