What options are available for measuring grounded thermocouples?
The only tried and tested method I used for monitoring a number of thermcouples that were an assortment of grounded and ungrounded devices of correctly and inadvertently-reverse wired types was to use a +/- 5 volt supply and a series of multiplexers (DG409) with cold junction measurement (RTD) and a voltage reference measurement also fed through the multiplexers. This then fed an InAmp with decent gain and mid-rail offset on the reference pin then to a decent ADC with serial interface.

Using +/-5 volts meant I could still read wrongly polarized/connected thermocouples and have a decent breadth of ground voltage. All the compensation was done in software with the voltage reference feed being used to compensate for any error introduced by the multiplexing.

If you are using several thermocouples then I can recommend this method but it was some years ago and maybe there is a reduced chipset version available.