How are taxi to and hold instructions given on an airport without taxiways to the runway end?
A is a taxiway, not the ramp. It will have stop bars and signs at the end. Here, the double solid lines are on the taxiway side and must not be crossed without clearance.

If the instruction is hold short, you hold at the end of Alpha.  

NB.  An active runway is never a taxiway.  The clearances and instructions are for runways, even when backtracking.

The initial clearance will likely be:


  Taxi via Alpha, hold short runway 07.


Followed by


  Line up runway 07 via backtrack and wait.


Then finally:


  cleared for take-off runway 07


The initial clearance might combine the first 2.


  Taxi via alpha, line up runway 07 via backtrack and wait


Note that the runway designator is always the departure runway so enter 25 and backtrack would not be used.