cosmwasm: ``Wasm contract requires unsupported import`` and how to work around it

I am writing a smart contract that needs to use some cryptographic crates out of my control. Unfortunately, those crates import and use the rand crate. Although the code compiles, and the .wasm file is generated, whenever I try to test it using cosmwasm-vm I get the error

StaticValidationErr { 
msg: "Wasm contract requires unsupported import: \"__wbindgen_placeholder__.__wbindgen_throw\". 
   Required imports: {\"__wbindgen_externref_xform__.__wbindgen_externref_table_grow\", \"__wbindgen_externref_xform__.__wbindgen_externref_table_set_null\", \"__wbindgen_placeholder__.__wbindgen_describe\", ... 13 more}. 
   Available imports: [\"env.db_read\", \"env.db_write\", \"env.db_remove\", \"env.addr_validate\", \"env.addr_canonicalize\", \"env.addr_humanize\", \"env.secp256k1_verify\", \"env.secp256k1_recover_pubkey\", \"env.ed25519_verify\", \"env.ed25519_batch_verify\", \"env.debug\", \"env.query_chain\"]." }

I have tried to work around this issue by stripping away all use of rand functions and structs, but even leaving in something as simple as the rand::Rng trait, triggers the above error

The rand crate is deeply embedded into those crypto crates, and it would be a titanic effort for me to make that dependency optional, hide all the related code behind an optional feature and hope for the changes to be accepted upstream. On the other hand though, I am pretty sure that the functions I need from those crates do not make use of any rand-related functions.

My question is: is there a way for me to declare inside my contract code, those unsupported import functions so that when the wasm is loaded, cosmwasm-vm does not complain and it can carry on?

Using the wasm2wat tool I can see that, for instance, the 1st function __wbindgen_placeholder__.__wbindgen_throw appears as

  (import "__wbindgen_placeholder__" "__wbindgen_throw" (func $_ZN12wasm_bindgen16__wbindgen_throw17h8d8353266d312eeaE (type 5)))

where type 5 is

  (type (;5;) (func (param i32 i32)))

so it there a way for me to write something like

#[no_mangle]
pub mod __wbindgen_placeholder__ {
    pub extern "C" fn __wbindgen_throw(a: i32, b: i32) {
        panic!("__wbindgen_throw")
    }
}

and have cosmwasm-vm pick it up and use it to fullfill the missing import?