MLM spillover/spillUnder function

Do you know anything about MLM coding? i need good php/mysql codes to make my portal do spillover feature.. All users will only have a maximum of 2 downlines,for example,assuming userA already referred 2 downlines, if a third person tries to signup with with userA's referral link,such a user should be placed under a different sponsor who doesnt have 2 downlines yet. can you do it? I will build the mlm portal/website myself,i only need good codes for spillover function, this is the only coding i need from you.shouldnt take more than 1hour if you know mlm coding.