Linux – Tool for Measuring Entropy Quality

If this is indeed due to address randomization (ASLR has to do with where the program is loaded, see here: http://en.wikipedia.org/wiki/Address_space_layout_randomization) then you can disable it by passing norandmaps to the kernel in the boot options (see here: http://www.linuxtopia.org/online_books/linux_kernel/kernel_configuration/re30.html).

As the Wikipedia page says:

It is also possible to write to /dev/random. This allows any user to mix random data into the pool. Non-random data is harmless, because only a privileged user can issue the ioctl needed to increase the entropy estimate. The current amount of entropy and the size of the Linux kernel entropy pool are available in /proc/sys/kernel/random/, which can be displayed by the command cat /proc/sys/kernel/random/entropy_avail.

So, in your case, if you are really intent on injecting some randomness obtained from the RaspberryPi as a file, then all you need is to write the file into /dev/random with a simple "cat randomfilefromrasp > /dev/random". What would be more complex (and require extra rights) would be to assert that the extra randomness ensures some given value of extra "entropy". But it matters only for the irksome blocking mechanism of /dev/random (this device tends to block when it supposes that it has burnt all its entropy); your extra file still gets added to the mix and will contribute to the actual entropy (i.e. you do get the security benefits, even if the kernel does not notice it).