You can create a GlobalPatron form and have that form hosted purely inside your internal network behind your corporate firewall so that nobody can view or submit it except for staff inside of your network.
To do this, create your form at GlobalPatron.com like you normally would. Then go to the "Share" tab of the form, and download the source code of the form by clicking the blue "Download Forms Code" button.
This will give you a zip file of all of the forms HTML/CSS/JS/JSON needed for the form to render and function properly which you can unzip and host on your own IIS server (or any web server), on an internal IP address that is only accessible to internal staff.
Once you have the forms code you can then disable the online form instance (or delete it completely).
Now that the forms code is on your server you can now write your own JS functions to override the default "submit" behaviour. E.g. override the submit buttons behaviour to instead post to your own internal-only web-service by overriding the definition of this method: window.globalpatron.editorpage.startSubmitting(); with your own definition.
function startSubmitting() {
//update UI
$(".submitting-body-content-placeholder").show();
$(".main-body-content-container").hide();
//get the form submission data
var postedJSON = JSON.stringify(getSubmissionData());
//call your API with the "postedJSON", for the save to be attempted
// here post the forms JSON to your own web service
}
Note: Alternatively, to securely restrict a form to certain staff you could also simply enable login protection on the form, and set your staff's email addresses as the only people with access to the form, however if you wish the entire form itself to only be accessible inside your corporate office network on an internal/local IP address behind your firewall you would use the "Code Export" version of the form like described above.