As map said as far as i know you have to use the slide option built into the VST most decent VST's have it somewhere just need to figure out where it is... or you could try play a single note for like x amount of bars then export that single note as a wav, load it in edison and set loop points and save it with the loop points, then reload it into FLStudio into the sampler not the adio section set the ASDR to your liking, that way now when you play it in the piano roll it will use that sample as an instrument, so when you play a higher note etc it will automatically pitch it up... I believe it SHOULD allow you to slide it like a FLstudio plugin, although i've had issues with it in the past, technically if you make single note like 4 bar's long and you don't intend to have it held for a really long time you can skip out the loop in edison part, but if you wanna have like pads going for the entire track it's gonna need to be looped otherwise it will run out... if that makes sense... dunno if i've described it in the best way... so to summarise:
1. export a wav of a single C note of 4 bars
2. loop if desired
3. drag onto sampler (not playlist) i.e with piano roll and the blocks for kick hi-hat etc
4. open piano roll, slide it as you would a normal fl instrument