@Chewy, this is a good idea to aid in a faster-steeped custard. I think you'll be pleased with the results.
I recently made a big batch of Third World Custard by ThirdWorldOrder. Well made it in early January I think it was. I vaped a couple tanks and fell in love, but I thought it would be a great base for a variety of custard blends so I made a flavor only base. This allows flavor molecules to marry but does little to help with steeping once you use that in a fresh mix.
I have, however, made cream bases where I mix with PG and VG in ratios I would use for a final vape, leaving only that ratio to be altered slightly by the addition of my nic and other flavors. Then again I'm very easy going when it comes to the final PG/VG ratio - 35/65 is just as ok to me as 30/70. Depending on the added ingredients once this has steeped out, the final juice mix could be ready to vape immediately after making a mix with the base, or it could be limited to the time those ingredients normally steep. Either way, unless you're adding something like tobacco, chocolates, coffees, or some of the bakeries, most will be ready to rock in just a couple days or so.
That said, I will share that about 3 weeks ago I took some Medicine Flower samples I had and mixed them with PG to achieve 10% flavoring dilutions. Just last night I mixed a bottle of strawberry using 20% of the dilution I had made (so 2% original flavor). I tried it right after mixing and it was already good and steeped (meaning the usual rough edges were gone) and tasted as though the entire mix had steeped the 3 weeks. Now this isn't something I plan to do with a lot of those or other flavors, but I will say that this experience has shown me - for MF Strawberry at least - that the dilution in PG and time will achieve the steeping effect. But at the same time, this is a single flavor mix and I imagine if using two or more diluted flavors that had sat a while you'd probably have that smoothness, but flavor would still not be "finished" as those new flavor molecules would not be conjoined yet.
Do be sure to let us know the results of your experiments.