How to use external random number generator with java.security.KeyPairGenerator?

Basically I have a RNG providing random numbers into a database and I would like to use these random numbers when generating a key pair.

From my understanding so far, you can initialize the KeyPairGenerator providing a randomness source (SecureRandom object). Looking into SecureRandom documentation, I only see the possibility to provide a seed that will be used as a "base" seed when generating a seed (method generateSeed()). Am I correct ?

Do I have to create my own implementation of SecureRandomSpi class where the generateSeed() method would basically return a random number picked from the database ?

I would appreciate advices from someone with experience in this matter.

Thank you for your support.