Yes, you can show your payment form to the customer.
But you will need to confirm these orders manually.
To do this go to the Parameters.
Open the Payments settings tab.
Then do the following:
1. Enter the deposit amount.
2. Check the Accept other payment types checkbox.
3. If required, specify the payment instruction.
It will be displayed in the order cart.
4. Set the Auto-confirmation of orders paid using other payment types checkbox.
Then, customer orders will get Confirmed status.
Otherwise, they will be in the Pending status.
Optionally, specify the message on the screen after the order is made.
5. Enter the URL of your payment form to the URL of site to show in frame....
It will be shown in the iframe immediately after the completion of the order.
6. Specify a appropriate width and height for the form.
7. Save it.
Check the result.
There is a payment instruction in the customer's cart.
And after the order was completed, the specified page is shown in the frame.