fiori-tools-proxy how to replace path with another taget

I'm trying to use the fiori-tools-proxy to proxy every request that starts with a certain string and I want to replace that starting string with another one.

I'll try to write down an example: every request starting with /DEST should redirect to /sap and of course adding the first part of the URL. This is my ui5.yaml file:

specVersion: "3.1"
metadata:
  name: testapp
type: application
server:
  customMiddleware:
    - name: fiori-tools-proxy
      afterMiddleware: compression
      configuration:
        ignoreCertError: true
        ui5:
          path:
            - /resources
            - /test-resources
          url: https://ui5.sap.com
        backend:
          - path: /DEST
            url: https://myurl:8001
            client: "500"
    - name: fiori-tools-appreload
      afterMiddleware: compression
      configuration:
        port: 35729
        path: webapp
        delay: 300
    - name: ui5-tooling-transpile-middleware
      afterMiddleware: compression
      configuration:
        debug: true
        transformModulesToUI5:
          overridesToOverride: true
        excludePatterns:
          - /Component-preload.js
    - name: fiori-tools-preview
      afterMiddleware: fiori-tools-appreload
      configuration:
        component: testapp
        ui5Theme: sap_horizon
    - name: ui5-tooling-modules-middleware
      afterMiddleware: compression
builder:
  customTasks:
    - name: ui5-tooling-transpile-task
      afterTask: replaceVersion
      configuration:
        debug: true
        transformModulesToUI5:
          overridesToOverride: true

And here is where I write the proxy

 backend:
  - path: /DEST
  url: https://myurl:8001
  client: "500"

But writing it like this proxy every call that starts with /DEST without replacing it with /sap so for example /DEST/opu/odata/sap/... will be proxied to https://myurl:8001/DEST/opu/odata/sap/... but what I want to achieve is to proxy it to https://myurl:8001/sap/opu/odata/sap/...

One other thing before someone responds to this post, for what I'm trying to achieve with this project I cannot just change /DEST with /sup. I know it's the easy way out, but I cannot do that.

I have read the @sap/ux-ui5-tooling docs but didn't find examples that show a use case like mine.

The docs you linked say that the backend proxy is based on @sap-ux/backend-proxy-middleware

The docs of this package have an example on how to change the path to which a request is proxied.

configuration:
  backend:
    path: /DEST
    pathReplace: /sap