Clear the area on a nice sunny day when the snake will be able to quickly move out of the way and make a lot of noise before you start cutting.

Make sure to keep the cinderblocks there, and maybe even add some large flat rocks for it to sun itself on and to hide between.

If the cinder blocks don't fit into your landscape design, you might try replacing them with a pile or small wall of natural rocks. I'd place the natural rocks where you want them before you move the cinder blocks, wait a couple of weeks, them move the cinder blocks. i probably wouldn't move the cinder blocks all at once. This might give the snake time to get used to the real rocks, and might avoid sudden drastic changes to the habitat that could cause it to move away. I think you have a fair chance of not scaring the snake away. My guess if like most creatures snakes get used to their territories and don't tend to move unless they have to.

Try to keep some of the grass habitat for the snake until your garden is well under way, and then consider leaving a bit of it permanently near the rocks, with the addition of some vigorous perennials such as mint to give it definition and make it look more gardenlike.

The snake is probably finding insects and so forth in the grass and would starve if you remove all of it (depending on what else is in the area). It will probably be able to find food in your garden if you don't use poisons, but in the fall when you clear out the garden it will still need its origional habitat to survive until it hibernates. It may also take it awhile to become comfortable enough with your garden to explore it.