Hello Rodrigo,
Please check :
The Package for transaction RVND - Create Online Payment is FIBL_OPAY.
The Enhancement folder contains a BADI definition called 'FIBL_OPAY_POST'. Once you check the BADI definition; there is a tab for subscreen. I think it is possible to achieve the requirement using these techniques provided by SAP.
Please try to read some topics on the screen-enhancements in the SAP library; it can help you to find the solution. I am doing the same. 
Regards,
Tanmoy