I have a few padded liner shorts that work pretty well. One from Endura and Funkier. The Funkier stay in place really well. I also have a couple from the old Performance Bike website. The problem that I have found with the liners is not lack of support, rather the leg material riding up into the crotch. Not a good thing. Cycling pants are kind of like saddles, very individual fittings, takes some trial and error to get a product that is comfortable. Cannot overstate the importance of proper fit. I definitely moved to a higher cost of bibs, well worth it, for me.
I only use the liners in place of cycling shorts when out for casual and errand type rides.