First make a backup copy of the file script.slc, which is located in ..\ctp_data\default\gamedata. Then open up the original with any text editor and add the following lines:

trigger 'DOR_T_Give_Gold' when (IsHumanPlayer(g.player) && (player.1.gold<=200000))
{
AddGold(g.player,1000000);
}

Now everytime the human player runs out of gold (< 200000), he gets 1 million more.