Paymattic - read only custom amount field?

Does anyone know if it is possible to make a custom payment amount field read only? It looks like I can configure it to pull the default value from a user meta key which is good and needed for this particular use case. However, I don't want the user to be able to change the amount.

I can probably do this with some JavaScript but I'm curious if there is a simpler way to do it within Paymattic.

EDIT: I should have read the documentation more before posting. Paymattic supports adding custom css/js to any of the forms so adding a single line of JavaScript worked to make the field read only.

document.getElementById("wpf_input_731_custom_payment_input").readOnly = true;

Leaving this here in case anyone might benefit from the info.

Thanks!