Defining the Turbomole named BP86 functional in Gaussian
From the Gaussian 09 manual:


  User-Defined Models. Gaussian 09 can use any model of the general form:
      P2EXHF + P1(P4EXSlater + P3ΔExnon-local) + P6EClocal + P5ΔECnon-local
  
  The only available local exchange method is Slater (S), which should be used when only local exchange is desired. Any combinable non-local exchange functional and combinable correlation functional may be used (as listed previously).
  
  The values of the six parameters are specified with various non-standard options to the program:
  
  
  IOp(3/76=mmmmmnnnnn) sets P1 to mmmmm/10000 and P2 to nnnnn/10000. P1 is usually set to either 1.0 or 0.0, depending on whether an exchange functional is desired or not, and any scaling is accomplished using P3 and P4.
  IOp(3/77=mmmmmnnnnn) sets P3 to mmmmm/10000 and P4 to nnnnn/10000.
  IOp(3/78=mmmmmnnnnn) sets P5 to mmmmm/10000 and P6 to nnnnn/10000.
  
  
  For example, IOp(3/76=1000005000) sets P1 to 1.0 and P2 to 0.5. Note that all values must be expressed using five digits, adding any necessary leading zeros.
  
  Here is a route section specifying the functional corresponding to the B3LYP keyword:
  
  #P BLYP IOp(3/76=1000002000) IOp(3/77=0720008000) IOp(3/78=0810010000)
  
  The output file displays the values that are in use:

IExCor=  402 DFT=T Ex=B+HF Corr=LYP ExCW=0 ScaHFX=  0.200000
ScaDFX=  0.800000  0.720000  1.000000  0.810000 

  
  where the value of ScaHFX is P2, and the sequence of values given for ScaDFX are P4, P3, P6 and P5.


For BP86 specified normally, this looks like:

IExCor=  404 DFT=T Ex=B Corr=P86 ExCW=0 ScaHFX=  0.000000
ScaDFX=  1.000000  1.000000  1.000000  1.000000


Those 3 IOps don't completely define the functional, however, IOp(3/74) is also needed. See the IExCor field, which corresponds to Becke 1988 exchange (400) combined with Perdew 81 + Perdew 86 correlation (4).