Considering a couple of RNG hardware manufacturers use different names for device interfaces, perhaps it would be 'convenient' to have apps look for the environment variable RNG_DEVICE which gives the name of whatever device is used (rnadom$, random, rand, even lpt2...) or even a special file that is mixed periodically by a cron job (noiz.c?).
The assumption is that reads from that device would return "truly random" bytes (not from a pseudo-RNG), either from specialized hardware or a system-noise sampler such as noise.sys (DOS) or random.c (Linux, FreeBSD).
How software would handle not getting enough bytes is another matter, > perhaps left configurable to the app.
Rob.
My hack to PGP to support RNG uses the varriable RNGDRIVER, but is in config.txt, not the environment.