When you have 30 Coppers press [F1], 4
to will highlight the 30 copper hill. Place the hill somewhere,
and you will now have -320 Coppers. Save your track and reload
it. You should now have 0 Coppers. Press F1, 1 to
highlight the 0 Copper location. Use it to clear the hill, replacing
the hill with that ground. You should now have at least 320 Coppers.
Repeat this as many times as desired.
Strategy guides from GameFAQs