That is not how plasma stealth works. The temperature of the plasma determines the minimum frequency of RF that gets through.
So you have to use a higher frequency radar and make sure the temperature of the plasma is not too high in front of the radar. You don't have to put the radar on the nose.
For optical sensors you would be imaging off-axis. So you can put the sensors pointing, say, 30 degrees below forwards relatively far back and there will not be much plasma in front of the sensors as it comes from compression and not friction.
There's a NASA PDF floating around that cites ~7000 K as the temperature of a plasma in front of hypersonic aircraft and concludes that radar is feasible then.
So you have to use a higher frequency radar and make sure the temperature of the plasma is not too high in front of the radar. You don't have to put the radar on the nose.
For optical sensors you would be imaging off-axis. So you can put the sensors pointing, say, 30 degrees below forwards relatively far back and there will not be much plasma in front of the sensors as it comes from compression and not friction.
There's a NASA PDF floating around that cites ~7000 K as the temperature of a plasma in front of hypersonic aircraft and concludes that radar is feasible then.