Unless you're doing this with huge amounts of money and stocks that are definitely going to be locked up for years anyway it's probably easiest to get a margin loan instead. You would maintain liquidity and still get a low interest rate if you use a broker like Interactive Brokers where the rates are just the fed funds rate +.25-1.5%. That's where I have all my money and I can take a loan against my assets whenever I want up to the full amount of margin maintenance, pay it back whenever I want, and pay no fees except around 2% APR interest.
If there is a benefit to a securities based lending account that goes beyond what you can get with a margin account I'd be interested in hearing about it, but I can't really imagine what that would be.