I don't think so. Google and Apple control the markets. I know of no way to sell software for Android or iOS that doesn't use their marketplace (and pay the price).
I use oziexplorer which is not in the app store. You download it from their website and pay them for a license. It is not without issues. When I switch devices I have to email them for a new serial number to unlock it.
I bought Poweramp (an audio player) years ago from their website. The code still works with the version from their site, but not the play store version.
Trying to be more privacy minded and now running an android device with no google. This of course means no playstore. Getting access to side loading free apps is no biggie, but paid is another story.
There are payed programs where you can sign into your google account then transfer the apps to a connected device. It doesn't give you an apk that can be shared. In my experience some simple apps worked but many did not. JRiver stuff didn't last I tried.
I would love to be able to side load JRemote and JRiver and I hope they will consider it. It would be easier than making a new app for Linux phone or my 2010 blackberry.
For remotes the most elegant way to do it would be to add a remote tier to the master license so you could just use your MC code to activate it on android. Another option would be to make a free version of the remotes that only works with MC when MC it is licensed for remotes. The later wouldn't work with JRiver for android though.
One obvious upside to side loading is JRiver would get 100% of the app purchase. Another is that people like myself would repurchase the app. A downside is that keys could be shared online, but would that hurt more than the cut from google?
In the interim you could try Upplay on a linux PC as an audio remote.