I don't see why download play would have kernel access.
As per 3dbrew, and my own foray into poking at dlp:
Dlp files are stored in cfa files, which dont contain code, just a romFS. Inside that romfs is a .cia, which is the Download Play version of the game. You can install that .cia with DevMenu, or Big Blue Menu, just fine, but it won't show up anywhere that you can launch it. the Download Play app won't show it, and DevMenu only appears to show Application type titles, not Child Types in the list. I don't have Big Blue Menu to test with, if it's even different that devMenu.
At the very least, Download Play has access to the am:u and/or am:net, which allows it to install the .cia files, which from my understanding of the process, isn't the same as kernel access at all. From what I saw of DevMenu's code, it looked like it basically just calls "StartCiaInstall", writes the .cia's data to to returned file handle, then calls "InstallTitlesFinish" which actually does the heavy lifting for installing it. There's a lot more to it, and I could be wrong, but from what I've read off 3dbrew, and what I managed to glean from devmenu's code, that's the gist of it.
Even if you could get a custom cia through, it wouldn't install on the target 3ds unless the sig checks were already patched, at which point you probably wouldn't need to be messing with DLP to begin with.