Or you can reverse integrate .NET4.5 into Win7 image, though as we know, it can be a lengthy process.
Or you can make a sysprep'd image. Install Win7 in a VM as .vhd format, apply all updates and install the latest .NET 4.5 installer. Then perform sysprep (OOBE->Generalize->Shutdown). When done, mount the .vhd file with Disk Management and then capture (via Imagex) the drive letter on which it is mounted and you'll have your install.wim. Then put that install.wim in a Win7 iso. Doing this is a more lengthy process than just doing an offline integration of updates, for example, but it has some advantages. You don't have to worry about any pending updates situation, for instance. I think the ngen run for .NET seems to not happen from the sysprep'd image when including .NET 4 (make sure you run the ngen though). I'm actually working on making a sysprep'd Win7 image right now with IE10 included. What I did this time is clone the VM (I use VirtualBox) before I run sysprep (but with all updates/hotfixes applied) and then save that VM so I can use it later on (say, 2 weeks from now if I wanted) and install/uninstall updates and then sysprep from that again, which then is a pretty quick process. MS seemed to have done a really shoddy job with their Win7 SP1 iso, which is why I've been using Win7 RTM with SP1 integrated, and then performed sysprep on that to get the SP1 image. I cleaned reg up (which by then saved 1000 registry errors -- yes, as I said MS SP1 image is awful) and also noticed that the SP1 integrated ISO I made was several hundred MB's smaller. Anyway I've been using that as master image and every now and then do another sysprep image with updates/hotfixes.
True, if done entirely from scratch. But one could clone/save a VM install of Win7 SP1 without any updates applied, which would save you from having to install Win7 in a VM, at least. The installation of updates/hotfixes in the VM is not really any slower (although that could depend on hardware involved) and the sysprep itself doesn't even take a minute. The longest time is then taken by capturing the image (several minutes). Saving the iso with updated install.wim only takes a few seconds. The longest part would be to install Win7 in a VM, which can be prevented by having a VM of Win7 install cloned and ready to go for that purpose. I just captured my updated install.wim for Win7 x64 and it was 3.30gb in size with over 400 updates included (this one without .NET 4.x included). I also included an extensive hosts file (C:\Windows\System32\drivers\etc\) for safer surfing (see my signature for the one I included). EDIT: taken sig links down for now as I was approached by MDL mod that this requires approval from MDL Team
If you use Windows Update and you don't want to see anything listed as being needed after a fresh install, use the "Satisfy WU updates" option. By doing that, it will install/integrate all the updates needed so nothing will be shown as needed in WU. WU expects to see the updates installed in GDR mode for it to be "satisfied". It's not that it's better that way- it's just the way WU wants to see them.