maybe you could make a little adaptor board with a SiLabs or other JTAG-equipped chip on it, and use that as a kind of DIY "ICE"?
that would be DBO "done by others" since the adapter boards is abour 1/1000 of the effort put into the 'JTAG ICE'

I would be a bit weary of doing this since a) the SILAbs have 'floating' dedicated pins so, for every app you would need a different adapter (one if the UART is used, another if not). Also 'special initialization and such will be required. The real 'killer' is that SILabs use P0 as the special function port, so you would have to 'repin' you entire code.

YES, it can be done, bit will it be ICE? not quite, the 3V3 5V toleranht signals will time a bit different, a 1 clocker will not match a 12 clocker in speed (even at 1/12 the clock) and much more.

Actually I think this will confuse more than it will help.

NOW, if you have ROUTINELY flipped between the SILabs chips and the 'regular' chips you may be so much in tune with the differences that you can handle it.

Erik