Dual-display solution (other than ARandR) on Lubuntu/Xubuntu?

What you are asking is fully reasonable and sensible, and I wish I knew all details about X configuration to just tell you how. Basically, what you have is one Screen in one X display server, and what you want is either two servers or two "Screens" in one server. In either case, it'll require you to set up the X server configuration(s); the so named /etc/X11/xorg.conf.

In X land, you have names of format "host:display.screen" that refer to the software structuring for how programs make their output, whereas the actual physical outputs are known as "Monitors", that are tied to screens through "Heads". Thus, in your case, you have a single screen "localhost:0.0" with two monitors (VGA-0 and LVDS). Most often there is singularity in monitors and heads and screens and displays and hosts, and everything is easy, but this is not your case.

I'm afraid there is no short cut for this, by you need to learn about configuring X. Essentially: firstly, you obtain the default configuration that your X server is using in the absence of an /etc/X11/xorg.conf, by entering console mode, killing X, then starting X with a special command line that writes the configuration to a file. Next, you edit that file by adding a Screen stanza, and bind each screen to its own head.

Maybe that very, very brief outline helps you move forward. I'm out of time.