Actually, adding an additional pole can be as simple as finding a bias/protection resistor in series with a high impedance node in the signal path then adding a shunt cap to ground. For example, in the AD797 opamp based MC phono stage in AudioKarma there is a second opamp that actually performs the de-emphasis and it has a 390 ohms resistor in series with the non-inverting input that also is in the signal path from the first gain stage.
The resistor is there mostly to minimize offset in the second stage. Adding a 3300pF cap to ground from the "output" end of the resistor improves the RIAA compliance and also improves the RFI immunity of the second stage. Many LOMC preamps have a non-inverting gain stage followed by a non-inverting RIAA deemphasis stage and the changes can be readily made.
The second stage has much lower overload margins than the first stage due to the fact that it has boosted signal levels, especially in the bass.
Also, If it is non-inverting, the gain at HF of the second stage is asymptotic to unity so that, without the additional pole, the level of RFI well above the audio band is the same as that at the output of the first amplifier stage.
However, the overload margin is lower and the desired signals are much larger, so the chance of RFI causing a significant amount of intermodulation which can become audible is higher than in the first stage.
Incidentally, passive de-emphasis stages, placed between the amps which are operated in fixed gain, usually are better in this regard as they don't have the implicit HF zero that forces you to add the extra pole.