It seems like that WP plugin would work to issue gift certs to be redeemed in-person at your real-world shop, if you don't need the gift cert to be redeemable in your E-junkie cart. They only generate a scannable, visual QR code block to identify each cert, rather than an alphanumeric code that buyers could type into their cart (which you'd also need to set up as a Discount Code first). I presume the plugin's PayPal IPN support would need to verify the IPN with PayPal, so you'd probably want to bypass E-junkie and just use PayPal's own purchase buttons for that with manual IPN settings in your PayPal account (which E-junkie's buttons would override for orders placed through our system).
For selling gift coupons online to also be redeemed online, you might add some custom HTML in the gift coupon product's Message (HTML) field to mock up a certificate image within which the code could be displayed. E.g., you might use a 3-row/3-column table layout that displays slices of a certificate image in the edge/corner cells, with the actual code being issued displayed in the center cell using [%codes%]. Those edge/corner images would need to be served from a secure https: URL to avoid security warnings or non-display in the recipient's browser, so you could use our free SSLpic.com service to store those images at a secure URL.
If you'd like some help setting that up, we can recommend the competent, E-junkie-experienced developers listed in our directory here: