Hello Milan
Recently I have completed a paper entitled: "Fixation & Preservation of
Nudibranchia & other Mollusca".  It does not address this specifically but
is inner-related and as such may be helpful, where as it flows with some
applicable premises.  You should be able to move your specimens from the
Ethanol into Ethylene Glycol for a while to resolve your problem.

Here is a species list from 3 habitats which have been successfully removed
from Ethylene Glycol an dried without the removal of the soft tissues
(listed by habitat):
  Cold Methane Brine Seep
    Bathyneritae naticoidea  Clarke, 1989
    Cataegis meroglypta  McLean & Quinn, 1987
    Eosipho canatae  (Clench & Aguayo, 1944)
    Provanna sculpta  Waren & Ponder, 1991
  Hydro-thermal Vent
    Bathymodiolus thermophilus (Kenk & Wilson, 1985)
    Cyathermia naticoides (Warren & Bouchet, 1989)
    Lepetodrilus fucensis (Warren & Bouchet, 1989)
    Pachydermia Laevis (Warren & Bouchet, 1989)
  River Limet
    Ancylus fluviatilis (O. F. Muller, 1774)

If the soft parts are not removed from the shell you will find that the
animal shrinks minimally when dried.  In your case allowing saturation of
Ethylene Glycol - C2H6O2 (= 1,2-ethanediol) 70%, into the shell should
prevent them from drying and cracking.

I have successfully removed 90 mm "Bathymodiolus childressi" from 70%
Ethanol and reconstituted them in Ethylene Glycol successfully, however if
this is for dissection purposes, the tissues becomes soft and is prone to
tearing.  This has also proven out successfully on freshwater Bivalvia for
the same purpose.

If you do not have ready access to Ethylene Glycol you can make your own
substitute.  A simple Chemistry lesson places Ethylene Glycol as an Ester
(alcohol) half way between Ethanol & Glycerol (Glycerin).  As such simply
Mix 50/50 parts of Glycerin and Ethanol (Ethel Alcohol 70%) a stout 140
proof + white liquor such as Everclear works good for this.  Shake until
homogenous.  It is then ready to use, it will not separate, but it will
evaporate.

If you (or anyone else) would like a copy of the paper please contact me
privately at:
Leslie Allen Crnkovic, HARF-IMCS  [log in to unmask]