You can use an external URL instead of the default form URL generated by Bonita BPM Studio Form Builder.
First place the form file in the webapps root folder in the application server.
Then go to the Details panel of the pool or task, Application tab > Entry or Overview Pageflow pane, and select Redirect to URL. The URL redirect options will appear.
Change the redirection URL in the process to match the name of the form file that you have placed in the application server (Tomcat/JBoss) webapps/root directory.
If you select and define the return URL as a parameter, the return URL will be defined as a parameter of the redirect URL.