So, you have a curve with two end points, and you then want to expand the curve (doubling the amont of total vertices), but still have it as one complete curve? Like having half a circle then trying to stretch it bigger to make a full circle?

If I'm on the right track, mhcannon's suggestion or my own would still work, duplicate the curve and mess with its position, then attach it to the original curve, maya then sees the object as one single curve.

Under the [edit curve] menu there are a few tools that could help
Attach curves
Detach curves
Open/close curves
Align curvess
Rebuild curve

Have a quick look at the maya help to see what each of these tools does and if they could help you.