Current split-gpg implementation relies on programs being configurable to call an alternate gpg program. But there are programs that appear not to call gpg (eg. Debian’s dput), instead relying on the gpgme library.
I find it annoyingly difficult to get proper information there, noone seems to explicitly write whether the gpg binary is actually called by that lib, or how to select an alternate. Activating gpgme debug traces reveals the use of gpgconf and the calling of the gpg binary. gpgconf seems to allow settings some parameters, but apparently not the “component”'s executable name. But even that tool is “designed not to be invoked manually by the user, but automatically by graphical user interfaces” – that makes me even more nervous. A quick look at the code does not make the thing any clearer, and there does not seem to be any envvar to override the choice.
I’m pretty baffled having to dig so much for such a simple feature, and pretty annoyed coming up with what looks like a post for a gnupg support forum 
– but maybe someone around here got to see what I apparently cannot, and already got SplitGPG working for this ?