Generate Scanlines with HTML5 Canvas and Javascript and apply CSS override to bottom of stylesheet to keep DOM clean of inline styles.

Scanline.js

/*
 * Created by Jordan Hess @jojohess
 * http://robotvictory.com
 * 
 * Usage:
 * On Window Load/DOM ready, trigger:
 * 
 * Plain JS:
 * scanline('article.dark div.sub_block',"rgba(255,255,255,0.05)",3,'45');
 *
 * OR
 * 
 * jQuery:
 * $('article.dark div.sub_block').scanline({ color: 'rgba(255,255,255,0.05)', spacing: 3, direction: '45' });
 * 
 * Enjoy!
});
*/

function scanline(sel,col,os,dir,lw) {
	os=os||3;dir=dir||'45'; lw=lw||1;
	var g, v = document.createElement('canvas'), n = v.getContext("2d"); v.width = os; v.height = os;
	document.body.appendChild(v);
	for (var x = 0; x <= os; x += os) {
		var a=x,b=0,c=x,d=os;
		switch (dir) {
			case "0":
				a = 0; b = x; c = os; d = x;
				break;
			case "45":
				c = x-os;
				break;
			case "90":
				break;
			case "135":
				a = x-os;
				break;
			default:
				c = x-os;				
		}
		
		n.moveTo(a, b);
		n.lineTo(c, d);
	}
	n.lineWidth = lw; n.strokeStyle = col; n.stroke(); g = n.canvas.toDataURL();
	try{document.styleSheets[0].insertRule(sel+"{background-image:url("+g+");}",document.styleSheets[0].cssRules.length);}catch(e){}
	document.body.removeChild(v);
}

if(jQuery) (function($){
	$.extend($.fn, {
		scanline: function(o) {
			var def = { color: '#fff', spacing: 3, direction: '45' }; o = $.extend(def, o);			
			scanline(this.selector,o.color,o.spacing,o.direction);
		}
	});
})(jQuery);