Of course it can be done.
You'll need the halyard
back to the cockpit. But also two lines for EACH reef; luff and the leech. (If you have the ketch
H28 your mainsail
may be small enough to justify experimenting with a single
line reef system but in my experience there is too much friction).
Typically you will have to change the luff reef as it is probably set up to pull the cringle down over a horn or hook. Using a line attached on the side of the mast
below the boom level the line feeds up through the cringle and down through a fairlead on the opposite side of the mast
then back to the cockpit this will ensure it pulls the reef forward.
The leech reefing line is probably already set up to exit at the front of the boom so that just needs to extend back to the cockpit.
effectively you will want to set up two reefs
. If it's a ketch
then you can probably strike the main if you need less sail.
You will want to set up lazy jacks to hold the bunched sail. And also you probably have a gate in the mainsail
track to remove the slides for the old reef system...you will need to make a closure for this gate so the mainsail slides stay captured.
The downside is that the halyard is no longer at the mast when you need to pull the sail right down so you have to watch how it is stowed in the cockpit to let it run out otherwise you're back and forward to untangle it when you pull the sail down.