Using a Web-based installer to retrieve (not distribute) 3rd party GPL or non-free software

Using a Web-based installer to retrieve (not distribute) 3rd party GPL or
non-free software

I am developing a software product which is able to communicate over a
command line interface with GPL-covered software (specifically, my
software can feed commands to FFMpeg). I understand that a crucial aspect
of the GPL license is whether or not you distribute GPL-covered
applications. My goal is to allow my users to have a seamless experience
installing both my software and 3rd party GPL software. But I am trying to
do this without my software actually including the the 3rd party
(GPL-covered) software. To do this I am considering Web-based installers.
I could use a Web-based installer to allow the end-user the option to
retrieve a GPL-covered or non-free software app from a totally different
server, independent of my own and outside my control. The user would be
the one to install the software simply by making a decision (i.e. pressing
"Next" in my installer). If they chose to do so, then my software's
Web-based installer would retrieve the 3rd-party software, decompress and
install it, then move on to installing my own application. In this way, my
installer doesn't ship any GPL-covered or non-free software, and yet from
the user's perspective all they had to do is click Next... Next... Next...
Done!
I have read about the GPL allowing you to distribute GPL-covered apps as
part of an "aggregate..."
http://www.gnu.org/licenses/gpl-faq.html#MereAggregation
...but this scenario isn't that. It's allowing the user to retrieve
applications or libraries at his own discretion, using his own bandwidth,
downloading from a server that has nothing to do with me.
I can't seem to find information anywhere about the GPL-related licensing
implications of using a Web-based installer. My goal is simply to give the
end user every high-quality transcoding option possible within FFMpeg
without stepping on anybody's toes legally.
Possible? If so then I'm hoping someone might be able to point me to a
software installer program that would facilitate this. Thank you in
advance for any replies.