[yarg]

You could use the biased distribution to build a lookup table for a less biased distribution.

Build a 10^n lookup table with an entry for each of the possible (ordered) n-tuples of values, give each entry a weight of the product of the probabilities of each of the n values making the entry.

Create a set of probabilities for each output and initialise to zero, run through each of the generated tuples in descending order of weight, set the lookup value to the output with the current lowest probability (or the first, or feed in another PRNG - but you have to stop somewhere) and increase the probability according to the weight associated with the tuple.

At the end of this process you'll have a PRNG that's at least as good as the input (and generally better) - although you'll need to query the seed PRNG n times per result. The higher the value of n the better the output (Although the lookup table will become quite large).

[yarg]

This solution gives no consideration to security only the distribution of outputs.