Below is the text that can be used to create your own .prq file for the Microsoft .NET Framework 4.6.1 Full Prerequisite.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<condition Type="2" Comparison="2" Path="HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full" FileName="Version" ReturnValue="4.6.01055"/>
<operatingsystemcondition MajorVersion="6" MinorVersion="1" PlatformId="2" CSDVersion="" Bits="4" ServicePackMajorMin="1"/>
<operatingsystemcondition MajorVersion="6" MinorVersion="2" PlatformId="2" CSDVersion="" Bits="4"/>
<operatingsystemcondition MajorVersion="10" MinorVersion="0" PlatformId="2" CSDVersion="" Bits="4"/>
<file LocalFile=".\\4.6\Full\NDP461-KB3102436-x86-x64-AllOS-ENU.exe" URL="" CheckSum="864056903748706E251FEC9F5D887EF9" FileSize="0,67681000"/>
<execute file="NDP461-KB3102436-x86-x64-AllOS-ENU.exe" cmdline="/q /norestart" cmdlinesilent="/q /norestart" returncodetoreboot="1641,3010"/>
<properties Id="{B1C982A7-100D-4691-9DCF-F5986F404DD8}" Description="This prerequisite installs the .NET Framework 4.6.1 full standalone package."/>
<behavior Reboot="32"/>


The Conditions are set for 64bit only, Windows 7, Windows 8, Windows 10
The download location is good as of 18 January 2016. No telling how long it will last.

For those new to making a Prerequisite .prq file:

On your desktop create a new text file.
Rename this file “Microsoft .NET Framework 4.6.1 Full.prq”
Copy the above text to this new file. (Between the +++++)
Move this new file to folder C:\Program Files (x86)\InstallShield\2015\SetupPrerequisites
Open any InstallShield project
Go to the Installation Designer tab > Application Data > Redistributables
The list should now contain the new entry “Microsoft .NET Framework 4.6.1 Full”
To the right of the list it will say “Needs to be downloaded”
Right-click on the item Microsoft .NET Framework 4.6.1 Full.prq and select Download Selected Item…
This downloads the 66 MB file to C:\Program Files (x86)\InstallShield\2015\SetupPrerequisites\\4.6\Full\
You should be good.

To edit any of the Conditions:
Right-click on the item Microsoft .NET Framework 4.6.1 Full.prq and select Edit Prerequisite