I just got a BMX bike today to convert to a mini-velo. First I want to get a seatpost that's long enough. Looking around, I found I can get a FSA 27.2x420mm seatpost for $25. With that and my Velo Webspring saddle, I think it will be enough, but I'm not sure. To get that one to fit, I'd need a shim, as the original is 28.6mm. Is it possible to use the shim in a way to extend it more? If not, anything else I can use to get a bit more length? Should I just find a pipe at the hardware store that will fit instead?