first of all, full tilts have no insole whatsoever. they have a rubber or plastic boot board and the heat molding liners, but no insole. i bought used dropkicks that weren't heat molded and i didn't mold them either, and i've had pretty good luck. however, i've heard that molding is the only way to get the liner to fill in small spaces between your foot and the liner. they will pack out to your foot shape no matter what, but heat molding is much more...accurate?
hope that makes sense. heat molding is definitely superior to letiting them mold just by riding them. if you buy online, you're going to have to pay extra to get them molded, so its up to you.