I am considering trying one of these, or making something simular:
Used to easily connect a one-way flow valve between your high pressure tank and your small pcp compressor allowing you to start the compressor without the back pressure in the tank damaging the compressor
airtanksplus.com
or
Best Fittings One Way Valve for Compressor / BEST Fittings One Way / Non Return Valve Quick Coupler Compressor Connector Decanting / Compressor Connector with One-Way Valve
submoa.co.uk
The one way valve keeps pressure off the compressor side so you can stop the fill, bleed the line, let the compressor cool and then resume the fill without having to mess with constantly opening and closing the valve on the tank. I have a small 90ci Guppy Tank and this should allow me to fill it with my small portable compressor (another variation of what you have). I have spoken to a couple people who have them and they claim they do an excellent job of filling a tank with a small compressor.
I can tell you I snapped the piston shaft on one of these type of compressors by not releasing pressure before restarting it to continue filling my air tank! The motors on these create a lot of torque, and let's face it, they are cheap Chinese machines made with cheap Chinese parts, so you do need to take every precaution you can to keep them running.