You can successfully cap a filled mold with piped chocolate if you work in a spiral from the outside, the chocolate will "float" to an extent. You have to pipe quickly and leave the molds somewhat under filled. This works best with a thicker liquid such as a coulis.
Foodpumps technique though rather archaic is a very good one and seldom used these days, the idea is to have your mixture partially crystallized, the cornstarch helps to accomplish this by drying the surface. After enrobing the crystallized form in chocolate, the moisture % is high enough to then re-melt the sugar after a day or so.
Here is the recipe for both ways, Filled chocolate molds and the cornstarch method.
750 g sugar
250 ml water
1 tsp or 5 g glucose
Cook until 110-112 C'
Cover with a damp towel then a lid. Let this cool for 5 or so minutes.
Pour your desired liquor into a clean bowl 250 ml for less sweet liquors Like Cognac and up to 325 ml for something like Cointreau.
Slowly pour your syrup mix over the liquor and then into a second container. Pour the mix back into the first container.
Let the sugar syrup cool to 95 degrees then you can slowly pour it into lined chocolate molds, do not fill them up all the way though.
First things first, you need to dry a quantity of cornstarch sufficient for your needs, this is best done in a low oven 60 C' for a FEW DAYS.
Sift this well and keep airtight.
When your molds are filled warm the cornstarch and sift it over the top of the chocolates about 1-2 mm thick. Let this sit at room temp for 24 hours. Carefully brush off the cornstarch and cover the tops like regular chocolates do not break through the crust.
If you want to mold them in cornstarch you will take a square cake mold and fill it with the dried cornstarch that has been reheated to 150 C', pack it in well and level the top. Now press in your mold shape and carefully remove it, repeat this as much as necessary to fill your form. Now fill this with your syrup (in this case the syrup must be hot) Sift the cornstarch over the top until it is 1 cm thick. Let this sit 3-4 hours then carefully flip it over, let it rest for 2 days. Turn the container over again and carefully remove the candies, brush the cornstarch off carefully and dip them in chocolate.
Simple really. Have fun.