Oxygen regulators, medical type

I'm looking for an inexpensive oxygen system for occasional flights up to 18,000 feet MSL. It seems easy to get a used medical type bottle with a regulator that includes a flow restriction built in. You can select, e.g., a 1 lpm flow rate right on the regulator. But, in a glider, you won't be able to reach this control when it is mounted behind the seat. My question is: with this type of regulator, if you add a flow valve and meter downstream, between that regulator and a cannula, and you open the flow on the medical regulator, but shut the added flow valve (unless and until you reach an altitude high enough to need oxygen), will the flow restrictor on the regulator protect the low-pressure hoses from excessive pressure, or will pressure build up enough to pop the hoses?

A side question is how to re-fill such a bottle.