Here are my steps for installing Windows7 from a DVD on a new MacMini via bootcamp, without needing an external DVD drive for that mac, as always YMMV.
1. A windows DVD
2. Another Mac with a DVD drive, e.g. your MacBook Pro (if you need to make the ISO)
3. USB storage of 4GB or more (SD cards don’t work directly, but work through a USB reader).
Copy the ISO onto your MacMini however way you can.
Run Bootcamp, it will prompt you to select the ISO, and the USB storage, and take it from there.