SPLat provides a mechanism for returning from a subroutine, then later resuming the subroutine at the next instruction.  Here’s an example:

wCallbackAddress   defWORD          ;memory to hold the resume address

   ...
   GoSub       subMySubroutine      ;start the subroutine
   (Suspend brings us back to here)
   ...
   GoSub       subDoCB              ;go jump to the registered routine
   (Will Return here)
   ...


subDoCB:
   Resume      wCallbackAddress     ;jump back to the subroutine
   (if we're here, it means there was no callback, ie wCallbackAddress is 0)
   Return


subMySubroutine:
   ...
   Suspend     wCallbackAddress     ;save the address in the variable
   (Will Resume here)
   fLoadW      0                    ;you can erase the callback address..
   FixToMem16U wCallbackAddress     ;..if you don't want it called again
   ...
   Return                           ;exit the subroutine, goes back to the Resume