Basically you would use a DAC as the offset to an OpAmp summer that
is passing the generator signal. This would be an offset between
ground and Vdd, so now you have to use 1 external OpAmp with a
negative supply and a fixed offset to shift the PSOC developed signal
so it is symmetrical about ground. This is nothing more than another
summer, but external.
There are a number of ways to develop - supplies, see attached, as
well as various charge pumps, switchers, etc.. TI, NSC, Philips, On,
You might also look at audio amps, as they have a power output stage,
thermally and current protected, are consumer cheap, and have OpAmp
like front ends in many versions.