Well, not to give out too much information...... BUT, you would use liquid plastic. Make a mould and fill in the hole sand and repaint.
It is most definetely a "easier said than done" project.
I have not completely filled in the stock clock location but this picture can tell you what it would closely resemble.
You put together a nicer stock looking dash than this.... you're in the wrong buisness!!!
Here's a few other angles of what a "filled in dash" would resemble
Notice the airvent on the left hand portion of the dash. The gauge that resides where the AC vent 'was', is smaller than the stock AC-vent hole. (Jeesh... did I explain that correctly?)
We will fill your 'stock-clock-hole' (somethin' funny about that.. I haven't figured out yet) so well that you will never know there was one there.
$150 plus shipping
Thomas Kenyon
Custom Sounds
San Antonio, Texas
210-340-4000