diff --git a/client.go b/client.go
index adbdd92..a8f731a 100644
--- a/client.go
+++ b/client.go
@@ -535,12 +535,42 @@ func PassthroughErrorHandler(resp *http.Response, err error, _ int) (*http.Respo
 
 // Do wraps calling an HTTP method with retries.
 func (c *Client) Do(req *Request) (*http.Response, error) {
+	return c.DoFunc(func() (*Request, error) {
+		// Make shallow copy of http Request so that we can modify its body
+		// without racing against the closeBody call in persistConn.writeLoop.
+		httpreq := *req.Request
+		req.Request = &httpreq
+		return req, nil
+	})
+}
+
+// Do wraps calling an HTTP method with retries.
+//
+// Usage:
+// import (
+//   ...
+//   v4 "github.com/aws/aws-sdk-go-v2/aws/signer/v4"
+// )
+// ...
+//
+// resp, err := client.DoFunc(func()(*retryablehttp.Request, error) {
+//   req, err := http.NewRequestWithContext(...)
+//   signer := v4.NewSigner(...)
+//   signer.Sign(ctx, req, ...)
+//   return retryablehttp.FromRequest(req)
+// })
+func (c *Client) DoFunc(f func() (*Request, error)) (*http.Response, error) {
 	c.clientInit.Do(func() {
 		if c.HTTPClient == nil {
 			c.HTTPClient = cleanhttp.DefaultPooledClient()
 		}
 	})
 
+	req, err := f()
+	if err != nil {
+		return nil, err
+	}
+
 	logger := c.logger()
 
 	if logger != nil {
@@ -655,10 +685,10 @@ func (c *Client) Do(req *Request) (*http.Response, error) {
 		case <-time.After(wait):
 		}
 
-		// Make shallow copy of http Request so that we can modify its body
-		// without racing against the closeBody call in persistConn.writeLoop.
-		httpreq := *req.Request
-		req.Request = &httpreq
+		req, err = f()
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	// this is the closest we have to success criteria
@@ -668,7 +698,7 @@ func (c *Client) Do(req *Request) (*http.Response, error) {
 
 	defer c.HTTPClient.CloseIdleConnections()
 
-	err := doErr
+	err = doErr
 	if checkErr != nil {
 		err = checkErr
 	}