You don't want to be using veg oil, veg glycerine can be used, but PG (propylene glycol) is better, concentrate seems to dissolve better in it, and it's thinner so it wicks better in ecig devices. Especially considering it can thicken up a bit once the concentrate is added.
There are quite a few different ways to make concentrate infused juice, look down a few threads and there is one with several pages where a few different methods are outlined.
My personal method is to first take a tiny amount of high-proof ethanol and dissolve the concentrate into this, using the least amount of alcohol possible, using a glass dropper works good for this. If you start with a crumble/dry bho/wax/budder/etc type concentrate instead of a shatter type it dissolves quicker. I then leave the glass bottle over heat for a little bit to evaporate some of the alcohol off, until the concentrate is reduced to a thicker, but still runny/slightly liquidly consistency.
Then I add the PG, of a ratio of 1 to 1, meaning with PG I match the volume of the thinned out concentrate. Keep it over heat, stirring until its mixed together. Let it cool down and it's ready to put into pretty much anything that takes regular ejuice. It's quite potent, as the total volume off the juice is only slightly over double that of the starting concentrate (50% PG, 45% concentrate, 5% alcohol)
With this method you do get a tiny amount of residual alcohol, so it's important to use ethanol, not Iso or anything else. E-liquid for ecig use has alcohol as a flavor base, or thinning agent quite frequently, it's perfectly safe to vape, especially in such low concentrations.
You can also dissolve the concentrate straight into the PG, but I've had worse luck with that. It took much, much longer to make, and I could never get it mixed completely. It would either separate or I'd have chunks in the juice. With the alcohol method you are basically loosening up the concentrate and allowing it to dissolve better into the juice, and if you evap the alcohol prior to putting the PG in (evaped until still runny, but most alcohol is gone) you get very little alcohol, but still a very well mixed stable product that's more potent than a lot of the methods I've seen.