Regulator design for negative voltage O/P
You could make your main inductor A coupled coil.Coupled coils are readily available off the shelf in SMD form from people like "coilcraft " .Keep the microhenries the same to avoid any other hassles and use the same current rating .You will find that the coupled coil wont be big or expensive .The 1st winding replaces the main inductor and the 2nd winding goes to a diode then a 10microfarad ceramic cap .The expected voltage is 7.5 because that's your output and the coupled coils that I have as samples are 1:1 .I recommend a LDO reg because the 7905 will struggle. If you don't want to do the coupled coil there is always the  "GEEBIG " which uses separate coils the second or added coil having a high inductance compared to the main inductor .Remember that these methods work when the neg power needs are much lower than the pos power needs which would be the case for your diode pump anyway .