I've just come up against this twice recently whilst bending crappy toys.
As mentioned usually a resistor equivalent to the speaker sorts it, but not for my burp-o-matic or hot-music so I had to wire their speakers internally into the new enclosures, and tap my line out off that.
This irked me, but I'm glad to hear sometimes that is the only option– thought it was just me being a dumb-ass....