Sorry for the delay in getting back to you, I didn't realize you had responded.
No, I am not referring to a custom gateway.
When an offline payment is manually applied the type of payment is selected from the drop-down box called "payment type" There is currently not an option to label a payment as paid by "check". The existing options include "Bank transfer", "Post transfer", "Cash", "Phone payment", "Fax payment", "Credit note", "Coupon", "Gift", and "Online by other means".
Please let me know if you need any further information. Thank you.