I mean you could inject your own sampling method into whatever shader/material you are using and manually clamp to a border color…
like
vec4 clampToBorderTexture(sampler2d ts, vec2 uv, vec4 borderColor){
vec4 c = texture(ts, uv);
if(uv>1. || uv<0.){
return borderColor;
}
return c;
}
that’s just off the top of my head though so dont quote me on it <3