Join two lines by adding straight lines and closing

[nic]

I have a macro that draws two non crossing curved lines as two seperate coreldraw shapes from data and want to join the two starting nodes and the last two nodes of the two lines by adding straight lines and then closing the resulting curve. The method of drawing the original lines prevents simply drawing a closed shape: As in order to keep the curve correct at start and finish a longer curve is drawn and then nodes are removed from the ends.

Any advice on how best to go about this would be appreciated - Please forgive that I havn't shown any of my attempts at doing this, trying to keep a little dignity.