See these links for attempts to get something like this change upstream,
but it's not entirely clear that this is the right general solution.

https://github.com/rust-lang/rust/pull/106017

https://github.com/rust-lang/rust/issues/106019

From f2b35ea1a09284cf30e75759a8727a3f84c352c0 Mon Sep 17 00:00:00 2001
From: Michael Benfield <mbenfield@google.com>
Date: Mon, 19 Dec 2022 20:30:19 +0000
Subject: [PATCH] bootstrap: use CARGO_HOME

---
 src/bootstrap/bootstrap.py | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/bootstrap/bootstrap.py b/src/bootstrap/bootstrap.py
index 2d5018d934e..4d202f969e3 100644
--- a/src/bootstrap/bootstrap.py
+++ b/src/bootstrap/bootstrap.py
@@ -811,7 +811,11 @@ class RustBuild(object):
                 print('      and so in order to preserve your $HOME this will now')
                 print('      use vendored sources by default.')
 
-        cargo_dir = os.path.join(self.rust_root, '.cargo')
+        use_cargo_home_env = 'CARGO_HOME' in os.environ
+        if use_cargo_home_env:
+            cargo_dir = os.environ['CARGO_HOME']
+        else:
+            cargo_dir = os.path.join(self.rust_root, '.cargo')
         if self.use_vendored_sources:
             vendor_dir = os.path.join(self.rust_root, 'vendor')
             if not os.path.exists(vendor_dir):
@@ -825,7 +829,7 @@ class RustBuild(object):
                 raise Exception("{} not found".format(vendor_dir))
 
             if not os.path.exists(cargo_dir):
-                print('error: vendoring required, but .cargo/config does not exist.')
+                print('error: vendoring required, but {}/config does not exist'.format(cargo_dir))
                 raise Exception("{} not found".format(cargo_dir))
         else:
             if os.path.exists(cargo_dir):
-- 
2.37.3