For some matters that are very sophisticated, give some thought to a radical alternative for your billing arrangement. Agree with the partner whose work you want most on the matter to pay that partner a reasonably significant premium on his or her standard rate for time worked on the matter. For example, 25 to 30 percent might be appropriate.
What you giveth, you also taketh away. The tradeoff is that no associates may charge time to the client on that matter. The purpose of this structure is to avoid training younger associates where little value comes to the client (See my post of March 15, 2006: shibboleth of institutional knowledge, yet high turnover rates; Dec. 17, 2006: obligation of law departments to train associates.) and to give the key partner an incentive to spend more time on the matter. Most partners are very busy and they will not over-bill time.
Even if this idea has merit, nothing about it addresses the logistical complexities of changing billing rates either at the law firm or with the law department’s billing system.