Try this:
Enter all the notes first, including the grace notes, and then tie them. Select the first grace note and press “S” (to create a slur). Click away from the slur to de-select it and then click on the first grace note and press “S” again. Go into Engrave mode and edit the positions of the two slurs by dragging their edit handles.
The position of the slurs will probably change if the spacing changes when other notes are added in later bars.
If you put the notes within the tie chain in alternating voices (along with their corresponding grace note) you might find that the amount of fixup required afterwards is reduced and the result a bit more stable than relying on Force Duration. You would have to remove rests in the passage of course.
Here’s the default result of inputting in the notes that way, voice colours shown:
And then with a little bit of slur tweaking:
Thanks!