I have had somewhat success fixing this issue on a friends GF FSDE 626. His 626 hatch had over 300'000 km's and would blow smoke at start up, hard acceleration from lights, and he had to top up the oil every few days. He was going to dump the car and I said let's try something and see what happens. He agreed as it was a nothing to lose situation anyway. If it doesn't work the car is going to be scrapped anyway.
We removed the old oil and put in oil designed for diesel engines only (not oil designed for diesel or petrol) and about 500ml of diesel mixed into the crankcase. He ran like that for about 50km's. We then changed the oil (was black as night) and oil filter and did the exactly the same again. Diesel only oil with 500ml diesel into crankcase with new oil filter. About 50 kms later he said it was getting better, so changed the oil and filter again but this time we put diesel oil only. Another 50 km's like that and we changed to 10W 30W normal petrol oil with new filter. The car hardly blows smoke at start up now, but a slight hint of blueish smoke when he guns it off the line every now and then.
This was done in October last year, and he is still driving it today with hardly any smoke from the engine anymore. So it worked for him. No guarantees this will always work and is something I would hesitate do on my engine if ever the issue was to arise on my FSDE. But there yo go. He spent a few $$'s on the oil and filters yes, (almost AU$400 all up) but it did improve the engine smoking issue.
I have read of people having success filling the crankcase entirely with diesel only - and running engine for 30 min or so, then doing oil and diesel mixture into crankcase, then finally oil only. But I was not game to try that.