Yeah it can be done if you can find a robust way to bias the bases of the BJTs. You'd need much less than 50K for the base bias resistance, especially at high frequencies. Injecting the signal into the base of each transistor using blocking caps would probably help too.
But using paralleled devices is probably easier, and I know it's what most laboratory amps use. For high operating voltages, you could use a driver based on MOSFETs, since there are many high power P channel FETs with Vds of 500V.
Also I wonder what you're trying to accomplish by driving +/-240V into a FET gate, besides destroying it?