I try charge pump with attiny85 1Mhz

digitalWrite(LED,HIGH);
delayMicroseconds(1);
digitalWrite(LED,LOW);
delayMicroseconds(150); // runtime delay
digitalWrite(LED2,HIGH);
delayMicroseconds(10);
digitalWrite(LED2,LOW);

With dirty trial and error experiments I adjusted, maximum run time is 150uS with 1Hz repeating 

Of course there is lot of possibilities to charge additional capacitor but unfortunately voltage rising very very slow and micro-controller can not start.

I think 150us is enough to send very short maybe 8bit packet with simple 433Mhz ASK/OOK radio

Success for 4 small diode power supply

It is time do design first more complex board :)