Triple black velvet is the holy grail of light absorption. You only really have to treat the first 5 feet in front of the screen
I attach black velvet to the walls around my portable screen.. goes in a hall way facing the living room though an arch way.
I use neodymium magnets sewn in the velvet and some tiny brad nails with grommets in the velvet... also on my screen skirt I used black Gaffers tape rather than sewing.Velvet on the walls that face the screen.
These magnets are so strong they hold on the steel corner bead under the plaster.
They work well for a stud finder to .. they grab the nails..
If your ceiling or beans has Nails or screws they will hold on them like glue.. Be creative it may look crappy when the lights are on, but then your take it down so no worries.
You say you have wood beams.. not sure which way the go, but if they go across the room in front of the screen you could us small brad nails put into the side of the beam then put grommets in the velvet to hook on the nails.
Wrap the velvet around the beam over to the last one that is close to the screen and hook on nails in the opposite side.. This would work with either orientation of the beams.. if you get what I am saying.
Be creative.. 5 ft out will help a lot!