I'm with Tosh on this one. Do not try this bypass idea, it will simply drain all the flow from your pole, especially when it is extended.
Maybe you don't quite understand what we mean when we talk about pressure switches. Basically it's a feature of most pumps so that if the flow is stopped at the pole end (eg by you turning off your little tap) the pump will stop too. It will re-start when the tap is opened again.
For obvious reasons, this is an ideal arrangement for water-fed pole. Actually I'd say it was essential, not just ideal.
If your pump doesn't have a pressure switch (some don't tosh), then ditch it and get one that does like this one:
http://cleaningspot.co.uk/acatalog/water_pumps.html#aDDP5800 for about £100
Then you will have no further problems.