You can glue reflector strips to fabric with "Goop" (any version, plumbing, shoe, marine...). This is really adhesive stuff, and will take more washings than you can imagine.

Don't forget good lights. For front, MagicShine probably offers the best bang for buck. Very bright for seeing the road and getting drivers' attention in front of you. For rear, DiNotte still owns the market (for the time being) when it comes to alerting distracted drivers coming up on your a** in daytime-dusk-night, rain- snow-fog, all-conditions riding.