That is really weird requirement, especially odd number of registers.
And no, openHAB binding will not do that natively, nor is it likely to do it in future.
Having said that, there is an obscure and rarely used binding feature “Advanced Write”.
We can apply a custom transformation that we create (usually javascript) to return some JSON that can describe a fairly arbitrary Modbus transfer. The binding makes a custom write transfer using this JSON “script”.
I think that could be used with a String Item to unpack data into a long FC16 block transfer. You’d probably want a write-only data Thing, and use “ordinary” data Things to split read data into separate Items.
You’d just have to decide how to pack your block of data - presumably from different sources - into a single String command, but that should be easy enough in rules. Comma-separated integer register values, perhaps.
This feature has been used for some equally weird devices that require writing to two different registers to “do xx”, it should work just as well with “write random block size”
You could of course use some external script instead to do all that and use the script with openHAB.