How to combine a LPF and a Voltage divider?
Your conceptual circuit does not really work, unless you really intended to place the low-pass filter corner at ~950Hz instead of 4.8kHz. As it is, your filter pole is being mostly determined by the voltage divider, not your 330Ω resistor.

Simply use the voltage divider and the value of its Thevenin resistance to calculate your filter capacitor. Your 2kΩ:4kΩ divider has a Thevenin equivalent resistance of ~1.3kΩ. So a capacitor of ~25nF would produce your expected pole at 4.7kHz.

You only save one resistor though.