I think the short answer is no. Many vendors will allow you to set your PG/VG ratios (Heather's Heavenly Vapes, Mt Baker Vapor, VapeDudes) for individual bottles, but sampler packs usually have a set PG/VG ratio and nicotine level. Your best bet is to either buy a sampler pack at their set ratios to determine your flavor preferences and then order larger bottles in your preferred ratio and nic level. Also, some vendors will send you a free sample with your order or with a coupon code. Mt. Baker Vapor will send you an 80/20 sample with your order, but I don't know if there is a minimum price point; I only ordered $20 of juice and got a free 5 mil bottle of another flavor. VapeDudes has a coupon code on their Facebook page that allows you a free 10 mil bottle in your preferred PG/VG ratio and nic level with your order.
Those are the vendors I'm aware of, though there are many I have yet to try. And I'm sure if you contact some of these vendors, they'll probably work something out for you.