You can also add other solvents to the mixture to effect the crystal shape. I would probably seed using crystals grown in a pentane mixture with ethanol
Step 1:
Use a mixture of heptane pentane with a cosolvent that encourages THCa to grow as needles and with longer terminations
Step 2:
Seed a mixture of heptane and pentane with the seeds from step 1. Grow big clear diamond shapes that aren’t just the normal heptane blocks