No it's not too late, but it's another avenue for infection.
You would need to boil it in some quantity of water before you added it.
If you currently have 5 gallons, it would take 1.67lbs of dme boiled in 1qt of water to raise the gravity.
W=N(1/(44/v))
W is the amount of dme in lbs
N is the number of pts to rais it (14 in your case)
V is the total volume (5 gallons plus 1 qt to boil DME in)
For LME replace the 44 with 36.
For big Belgians you traditionally add sugar after primary fermentation to hit higher ABVs, so yr not going to break anything by doing it with DME. Just sanitize everything, boil, cool (don't add boiling DME to your fermenter), and add.
I'd let it ride as is though. You risk aeriation (minimal since you are reintroducing fermentables) and infection. As it sits It should be a nice session beer around 3~3.25%. Call it a learning experience and brew another batch when your fermenter is available.