PGraphicsStack Proof of concept. Use a stack for PGraphics like pushMatrix() and pushStyle() in Processing.

pgstackExample.pde

PGraphicsStack pgs = new PGraphicsStack();

class PGraphicsStack {
  private ArrayList<PGraphics> pgList;
  private ArrayList<PVector> dimensionsList;

  PGraphicsStack() {
    pgList = new ArrayList<PGraphics>();
    dimensionsList = new ArrayList<PVector>();
  }

  PGraphics push() {
    return push(createGraphics(width, height));
  }

  PGraphics push(int w, int h) {
    return push(createGraphics(w, h));
  }

  PGraphics push(int w, int h, String renderer) {
    PGraphics pg = createGraphics(w, h, renderer);
    return push(pg);
  }

  PGraphics pushCopy() {
    PGraphics pgCopy = createGraphics(width, height);
    pgCopy.copy(g, 0, 0, width, height, 0, 0, width, height);
    return push(pgCopy);
  }

  PGraphics push(PGraphics pg) {
    pgList.add(g);
    g = pg;
    dimensionsList.add(new PVector(width, height));
    width = g.width;
    height = g.height;
    g.beginDraw();
    return g;
  }

  PGraphics pop() {
    g.endDraw();
    PGraphics pgReturn = g;
    g = pgList.remove(pgList.size() - 1);
    PVector d = dimensionsList.remove(dimensionsList.size() - 1);
    width = (int) d.x;
    height = (int) d.y;
    return pgReturn;
  }
}

void setup() {
  size(500, 500);
}

void draw() {
  stroke(0, 12);
  noFill();
  float d = random(width);
  ellipse(width / 2, height / 2, d, d);  

  PGraphics pg = pgs.push(width / 2, height / 2);
  stroke(0, 12);
  line(random(width), random(height), random(width), random(height));
  pgs.pop();

  image(pg, 0, 0);
  image(pg, 0, height / 2);
  image(pg, width / 2, 0);
  image(pg, width / 2, height / 2);
}