I've held my thoughts for a while know. First Swingdude, There are many different ways to tie in, you don't need to have a base tie off. I use 3 different tie in techniques depending on the tree and the work required.
Regs, I know exactly where your coming from. We have done storm damage work in White Pine trees the last two winters. most being in the 100-120 range. I never hit my final TIP and am normally doing multiple trees before hitting the ground. (most in one shot was 10) I've single lined the trees both years. To do so you either need a really long rope, 2 ropes, or an available ground guy. If a ground guy is not always available Ddrt might be your best option. One of the downsides to SRT is not being able to pull your line easily while up in the tree (with out aid from a ground person) and continue on. So for what your describing, without using a more complicated system your probably better off with what your already doing.
Saying that i will try my best to describe the easiest solution (you will need the Quick Release pin though) If you don't have it or don't want to get it this option isn't much of an option at all:
What i would suggest is set an access line as you already do. Ascend it whatever manner you prefer, taking your climbing line with you. You then continue to ascend same as you do now alternating between lanyard and climbing line till you reach your TIP. Once you reach your TIP install the rope wrench. Then tie into your TIP with either a running bowline or a
Monkey Tail Attach the tail of your line either to the Bowline or in the picture of the monkey tail to the biner (this is used to retrieve the system) I would also say i use a cabium saver in conjuction, makes retrieval smoother and i don't like sap. Your now in a loop system. This is why a quick release is required. Once you reach your next TIP or the bottom of the loop. Lanyard in remove the Rope Wrench and your climbing knot and pull the tail to retrive your tie in method.
The change of TIP is not as quick, with a little practise it doesn't take too long. In my opinion the time saved using SRT makes up for the time it takes to change TIP's.
This is just one method of many.
That was very long winded and kind of complicated. Hope its understandable. I want to make a Video of different tie in techniques but don't know how soon i'll be able to get to do it.