I'm not sure if the netlock of Tchibo's USB modems is actually limited to Tchibo SIM cards or only to O2 SIM cards in general but if your modem does not accept Lidl SIM cards Mobile Partner would just require an unlock code, which you can obtain free of charge from
http://a-zgsm.com/huawei.php within 30 seconds or so (depending on how fast you enter your device's IMEI).