I have a bunch of bright white cardstock. Is there something I can add to make it glossy like glossy card stock
Have you considered using a high-gloss clear spray paint?

And I would suspect that gloss = plastic to some degree, and an inkjet printer basically sets down ink droplets. If you print on glossy paper that's not specifically designed for inkjet printers, you might end up with a smear of ink. So I'd suggest do printing first, then if you use spray paint you could possibly do several pages at once. 

Bonus perk of post-print gloss: inkjet ink doesn't always stay put (can be smeared by malicious fingers), so glossing the paper afterwards will help seal that ink in.

HTH