There do exist converters that will change 240p to VGA 480p with no added lag or quality loss. They're expensive, but you could at least be confident that they would work.
How does the TV like 240p through other connections? If you're feeling adventurous, you could hook up the RGB color lines as-is to a VGA connector, then run composite video into an EL1883, which would split off the horizontal and vertical sync pulses for you to connect to the appropriate places. However, there is very strong chance that the TV would not like the low resolution. Also, you might need to invert the sync pulses to get them to work. It just depends on what the TV is happy with.
Of course, no interlaced content would work.
Does this TV have component video inputs? You can get a much cheaper RGB to YUV converter, and the quality will be almost as good. Assuming that 240p works in composite and s-video, it will work with component, guaranteed.