First of all, you can change workspace cycle hotkeys to something closer, Ctrl + Right \ Left Arrows are pretty good.
If you just want hotkeys to switch into specific workspace, here how you do it:
1 Add new hotkey entries to Screen / Screen (Global)
2 In Identifier field you should put wm.context_set_id
3 For Context Attribute you should use window.workspace
4 Use names of your workspace tabs in Value field
In my example I can switch into Fullscreen workspace with Ctrl + Up Arrow and into Materials workspace with Ctrl + Down Arrow.