param($name, [ScriptBlock] $getter, [ScriptBlock] $setter)

Add-Type @"
using System;
using System.Management.Automation;

namespace Lee.Holmes
{
    public class PSScriptVariable : PSVariable
    {
        public PSScriptVariable(string name, ScriptBlock scriptGetter, ScriptBlock scriptSetter)
            : base(name, null, ScopedItemOptions.AllScope)
        {
            getter = scriptGetter;
            setter = scriptSetter;
        }
        private ScriptBlock getter;
        private ScriptBlock setter;

        public override object Value
        {
            get
            {
                if(getter != null) { return getter.Invoke(); }
                else { return null; }
            }
            set
            {
                if(setter != null) { setter.Invoke(value); }
            }
        }
    }
}
"@

if(Test-Path variable:\$name)
{
    Remove-Item variable:\$name -Force
}
$executioncontext.SessionState.PSVariable.Set((New-Object Lee.Holmes.PSScriptVariable $name,$getter,$setter))