You are quite correct in that applying rig tension alone will not inherently cause the mast to pre-bend, at least assuming that your spreaders are free to rotate fore and aft.
If you have adjustable spreaders then you can use these to translate the rig tension into pre-bend if you wish. If you adjust them so that the shrouds are being deflected aft then rig tension will cause the shrouds to straighten forcing the hounds forward and bending the mast, depowering the rig and flattening the sail.
Or you can use chocks behind the mast if you want to get it to bend without applying kicker (eg for very light winds when you need the sails flat). As the wind strengthens you then switch to having chocks in front of the mast to prevent it bending, then in stronger winds remove them all together so that the rig can depower “on demand”, ie by applying kicker.
Remember to use the minimum allowable mast pin size (6mm from memory) which makes it a whole lot easier to get the settings you want without it becoming tight.
Another idea I had – though I’m not sure of the legality of this – was to elongate the pin hole horizontally either in the mast or in the tabernacle (or even in both) to provide the required range of fore and aft movement. Has anyone done this?