Extracting only the entropy
The best answer is almost certainly to use a cryptographic hash. 

Your reason for avoiding a cryptographic hash makes no sense to me.  Your problem does not explain the motivation for your question, but I suspect you've fallen prey to the XY problem (see also here).

You haven't told us what you're ultimately trying to accomplish, but I suspect the right answer in practice is ultimately going to be:


Use /dev/urandom to generate cryptographic-quality pseudorandom numbers.
If you have a source of entropy, feed it into /dev/urandom (e.g., cat somekindarandombits &gt; /dev/urandom), then see step 1 above.


Internally, this effectively uses a hash.

I also recommend you read the following:


https://security.stackexchange.com/q/89/971
https://security.stackexchange.com/q/3936/971
https://security.stackexchange.com/q/14292/971