I suspect the answer is you can't do what you want but you would have to explain better.
The splitter thing is a extremely simplistic device all it does it prevent the signals from the phone and the modem from interfering. It provides no other function. ADSL is something completely different than ethernet. Even though they may run over similar cable the methods they use are very different. Think of it being the ethernet speaks english and the adsl speaks spanish but at a hardware cable level. Your ADSL modem function is to act as a translator.