Forcing Apt to install binaries using packages for another release is a terrible idea, and will probably lead to tears and recriminations. Don't do this. Package installations are a convenience but they have their limitations.
I've seen references to hacks that allow this (JDK 1.7 version hacks spring to mind) but they are all fraught with potential disaster. Let us not speak of them again.
Your non-hack solutions:
Build from source. This will require the dev-essentials package, along with some dev-essentials skills. If you go down this route you pretty much have to go ask for help from the maintainers of the application if you run into problems. Expect to iterate on this until it is done.
Install VirtualBox and create a 18.x VM and install the software package on that. You can even set up persistent shared directories between the Linux host and guest OS to make this almost seamless.
Based on another Answer, I felt compelled to leave you with this nugget of wisdom:
(!) When pinning, you must ensure compatibility of packages by
yourself since Debian does not guarantee it. Note that pinning is
completely optional, and Debian does not encourage pinning without
(!) Seriously, don't do this. Doing this will break Debian and leave
you with a system that doesn't work and can't be fixed. Use Backports
Yeah. Don't do this. If Debian says not to do this thing, then Ubuntu shouldn't do it. This isn't Gentoo. (Oh snap!)