As far as using this circuit to switch a load, rather than as a linear amplifier, the only thing I can think of is an NPN transistor controlling the current to a PNP transistor's base, or the voltage across a MOSFET's gate, which in turn switches the load.

R1 holds Tr1 off, preventing any leakage through Tr2 from turning it on. It also helps to speed up the off time of TR1 by discharging its base, when Tr2 is turned off. It be a fairly low value, say 1k.
V
R2 = V
INPUT - V
BEI
R2 = V
R2/R2
Assuming Hfe for Tr2 is big and hardly any current flows through R1
Tr1_I
B = I
R2Example:
Suppose we need to switch a 200mA load and Tr1 has a low saturation voltage when I
B =
1/
20 I
C. The minimum input voltage is 4.5V
I
C = 0.2A
I
B = 0.2/20 = 0.01A
Calculate R2
I
R2 = I
B = 0.01A
V
BE = 0.7V
V
R2 = V
INPUT - V
BE = 4.5-0.7 = 3.8V
R2 = 3.8/0.01 = 380R. Use 330R.