Extracts are not easily handled in BeerSmith, yet. Their growing popularity makes that accommodation inevitable, but until then, you'll have to compromise a little.
Luckily, Northern Brewer gives us a key for calculating the bitterness of Hopshot. http://www.northernbrewer.com/documentation/hopshot.pdf
To get a 1 mg dose to project as 10 IBU, the extract has to carry 70,000% AA. But, most brewers use either ounces or grams, so you'll want to adapt that number to your preference.
The relationship of 2.43% AA = 10 IBU as 1oz makes sense, but why not turn the number into something you can use for both inventory and ordering? Why not make 1 ounce or gram equal an entire container of Hopshot? That way, anything less than a whole number is a percentage of the container.
So, one syringe of Hopshot is 5ml, or 50 IBU in 5 gallons (19 l).
As a gram, a Hopshot syringe would be 345% AA each.
As an ounce, a Hopshot syringe would be 12.17% AA each.