If you don't want to "fake" a sidechain, you have a lot of other options. The limiter, the peak controller, and the compressor are the standard ways to do it.
I personally use the peak controller to mute kicks so I can set up ghost sidechains. (No idea if that's the proper term, but the kicks still sidechain even when they're muted without messing with mixer routing).
The peak controller is the easiest to understand way to sidechain, so I recommend going with that. Here are the details of setting it up.
Route a kick to any mixer channel and open up the peak controller. By default, it will mute the kick, but if you want to unmute it, click that button little box in the corner.
Now, you have to decide what you want to sidechain. If you have another synth, for example, on another mixer channel, you probably want to sidechain its volume parameter. Right click the synth's volume slider and select "link to controller".
Under "internal controller", select the peak controller PEAK. (With LFO, or PEAK alone, doesn't really matter). Then hit the arrow next to the Mapping Formula underneath and select "inverted". This is the key to the sidechain. It will duck the volume of the synth every time the kick hits because of this inverted formula. Where it says "1-Input", click in that and change it to "0.8-Input". FL does a lot of stuff at 80%, so this is important to keep things consistent.
And that's about it. Your actual sidechain effect will depend on the sample you choose to do it and its various settings, as well as the settings you use in the peak controller. Ton of options from here. You can set up more routing, experiment with other formulas, samples, etc.