Using Well Pump 240 v Circuit For 110 v Light With Plug
Stop using ground as neutral. If your grounding system is anything shy of perfect, you'll energize everything that's supposed to be grounded. 

The fact that it has conduit on the ends doesn't mean it's entirely conduit.  If the line were direct burial, the descent to depth is required to be in conduit for physical protection.  *Push and pull the wire. If it has about an inch of relatively free play, then it's in conduit. 

Use a subpanel

If it is indeed conduit, then you can fish in THHN wires: two hots, a neutral and a ground, all #10. Bring that to a subpanel, and have a 20A double breaker in the sub power the well, and 20A single breakers feed convenience outlets and other 120V loads.  You will also need a local grounding rod, or rather 2 rods 10' apart unless your AHJ will let you use the well pipe.  AHJ=authority that issues permits and inspects. 

You can then upsize the breaker in the main panel to match the wire (30A for #10, 50A for #8 THHN). 

Otherwise... Use a transformer

For casual loads like you might plug into an outdoor receptacle, a 1.5 KVA transformer will suffice.  If you want a LOT of power out there, a 5 KVA 1-phase transformer off Craigslist will do.  Do not use a "step-up/down transformer" because that can accidentally put 240V on your hot and 120V on your neutral.  You need an isolating transformer.  For small loads like this, I would leave it isolated, i.e. don't bond neutral to ground. And have it feed a GFCI recep for statutory reasons. 

Why not bond?  Bonding (vs isolated system) is a double-edged sword.  An isolated system has no relationship with ground, so touching hot is harmless - power doesn't flow because there's no loop. On the other hand, bonding neutral to ground forces hot to be within 120V of ground, which protects you from leakage from the 7200V transformer primary.  But in this case, the transformer primary is + and - 120V from ground (summing to 240V), so bonding does not make it any safer. Therefore isolation affords better safety.