To add this item to your NWN2 character you can use the in-game console, the Silverwand Item Summoner, or purchase from the Silverwand Magical Emporium.

To add an item with the console giveitem command or the Silverwand Item Summoner you will need to know the item's tag, which is the part of the file name preceding ".UTI". After subscribing navigate to the appropriate sub folder in C:\Program Files (x86)\Steam\steamapps\workshop\content\2738630
If you look at the contents you can see which files are UTI files. If there is documentation you should read it,

Using the console giveitem command will disable achievements, so to reenable achievements save the game and then edit the file globals.xml in the saved game folder, changing the 1 to 0 (zero) in these lines (credit to Aldroen):
<Booleans>
<Boolean>
<Name>ShowCheatsWarning</Name>
<Value>1</Value>
</Boolean>
<Boolean>
<Name>Cheater</Name>
<Value>1</Value>
</Boolean>
</Booleans>

Fire and Ice composite bows are included in the Silverwand Weapons - Bows item in the workshop now.

Hey can you make a composite long bow like this that would be dope!