Create an extra partition on your with Disk Utility. Download Yosemite from Appstore. Install it on the partition. Reboot from it and do your things. Reboot from the normal partition.
- Launch Server.app
- Select 'System Image Utility' from the Tools menu of Server.app
- Verify that your partition appears in the header.
- Select the 'NetRestore Image' radio button, click 'Continue'
- Store the image in the directory /Library/NetBoot/NetBootSP0
- Enable NetInstall under the advanced options of Server.app.