4046 PLL and Differential Amp question

[Synthaholic aka sPEW]

One of the failings of using a 4046 PLL as a frequency multiplier is
that it's output is square.  I have an idea to get at least one more
waveform out of it.

The capacitor connects to two pins of the IC, neither of which is
ground.  That means the cap floats and a single ended approach would
probably not work.

First, I am assuming that the cap's integration voltage is not square.

If a high input impedance differential amplifier were used, it might
be possible to amplify the capacitor's integration voltage and supply
a single ended output.  Do any of you have part type suggestions?  I
am sure it will need to be a FET type at least.  Are there MOSFET
input opamps?

Or would the S/N ratio be so bad that this would be impractical?