During the two 'off' weeks, an ECA stack can be used as required. ECA will not cause such a pronounced down regulation and desensitization of the receptors, certainly not to the extent of clen. Ephedrine has a short half life in contrast to clen which results in times throughout the day where the betas will partially recover from stimulation by adrenaline and nor-adrenaline. Potency is also much weaker that that of clen, as it is not a specific agonist. Ephedrine is also thought to increase the conversion of endogenous/exogenous T4 to T3 through the activation of deiodinase enzymes responsible for this process. This is important as clen is known to slow the rate of T4 to T3 conversion. As a side note, some bodybuilders will use T3 concurrently with the Clenbuterol/ECA cutting cycle (together with certain anabolic/androgenic steroids no doubt!) in an attempt to at least maintain plasma T3 levels.
The other way to take Clenbuterol is to use it continuously over the course of the 8 to 10 weeks. Be aware that this will mean having to increase the dosage that you are using. At the same time, the benefit of this approach is that continued use ensures that your metabolism is constantly activated. Be aware that the same dose of the drug will last you up to 5 weeks of use before you have to up the dosage amount. With this approach, you will begin somewhere around 20 to 40 mcg a day and ramp it up by 20mcg intervals until you are done. This will keep your metabolism working at peak efficiency the entire time.