For years I shared a garden with a great neighbor. Need advice on fairly recent developments.

[Paper Roses]

My neighbor lives in an apartment building with a large yard next door to me. A new tenant as of 3 years ago, decided she needed to take control of all the gardening and has planted almost the whole area with stuff she wants.
Fine, can live with that. (She does not share)
My original partner in this venture and I have planted a few herbs and tomatoes, the new neighbor took over the rest. We are both alone so our needs are not great. It is a case of grin-and-bear it.

In an area near the garden I planted Friseé. I love it and have planted it before in our old garden. Since the spot I now have is tiny, I am wondering if I can transplant the thinned shoots of this wonderful lettuce to another spot. I planted the area from seed and the new plants are coming up nicely. I know they have to be thinned and that will be my project next week.

I have no yard to plant anything but wonder if I can plant the thinned shoots in a ground level window box. I have bags of soil and an area where I can place the box. Do you think this would work or should I just thin and throw away the new plants?
I hate to just toss them, Friseé costs about $5.00 a (very small) head--if you can find it--at local grocery stores.
Would love any advice,
PR