Using customized Random number in keypair generation in uECC_make_key method in micro-ecc - Riot OS

Question

I am trying to implement an elliptic curve scheme in micro_ecc, wherein the secret key is the addition of two random numbers and the public key is derived from the secret key as follows priv_key = (a+b) public_key = (a+b)G. I have checked the code in micro_ecc the key pair generation is defined in uECC_make_key() in uECC.c but it seems that the implementation cannot be modified to add any new elements. I have run the code in the pkg_micro-ecc-with-hwrng example given in the tests folder. Can someone tell me how I can randomly select the secret key and then generate the key pair as mentioned above? If micro_ecc in Riot does not support it, can I do the same in the relic?