Was testing some more and got it working with this code...
PHP Code:
new sprite = engfunc(EngFunc_CreateNamedEntity, engfunc(EngFunc_AllocString, "env_sprite"));
if(!sprite) return PLUGIN_CONTINUE;
set_pev(sprite, pev_classname, "spritetest");
engfunc(EngFunc_SetModel, sprite, "sprites/glow01.spr");
engfunc(EngFunc_SetSize, sprite, Float:{0.0,0.0,0.0}, Float:{0.0,0.0,0.0});
engfunc(EngFunc_SetOrigin, sprite, origin);
set_pev(sprite, pev_solid, SOLID_NOT);
set_pev(sprite, pev_movetype, MOVETYPE_FLY);
set_pev(sprite, pev_aiment, ent);
Still need to set some key/values to get it to look right ;p