.Net3.5 and Server 2012

I have tried several ways to get the .Net Framework 3.5 in stalled on Server 2012 however the only way that ever works every time and is supper fast is powershell.
 On the Server 2012 media is a folder called sources\sxs so from an elevated command window I run
dism /online /enable-feature /feature:netfx3 /all /limitaccess /source:f:\sources\sxs as per the screenshot below. F:\SOURCES\SXS is just whereever you have the SXS folder located.

Now I was working on a project with installs around the world and it was proving hard to get the media to all the different sites and I was wondering if copying just the .net3.5 cabs from that SXS folder would do the job as its only 18Mb but alas it didn't work and I had to go back to the full folder.  What I now do is to load the SXS on a network share and just use the network path in a powershell script.